Part 1

JOURNAL OF THE PROCEEDINGS OF THE LINNEAN SOCIETY.

ZOOLOGY.

VOL. IV.

LONDON: LONGMAN, GREEN, LONGMANS AND ROBERTS, AND WILLIAMS AND NORGATE. 1860.

PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.

LIST OF PAPERS.

Page

GARNER, ROBERT, Esq., F.L.S. On the Shell-bearing Mollusca, particularly with regard to Structure and Form 35

HANLEY, SYLVANUS, Esq., F.L.S. On the Linnean Manuscript of the 'Museum Ulricæ' 43

HUXLEY, Prof. T. H., F.R.S., F.L.S., F.G.S., Professor of Natural History, Government School of Mines. On the Dermal Armour of _Jacare_ and _Caiman_, with Notes on the Specific and Generic Characters of recent _Crocodilia_ 1

SALTER, S. J. A., Esq., M.B., F.L.S., F.G.S. On the Moulting of the Common Lobster (_Homarus vulgaris_) and Shore Crab (_Carcinus mænas_) 30

SANDWITH, Hon. H., M.D., C.B., Colonial Secretary of the Mauritius. On the Habits of the "Aye-Aye" (_Cheiromys madagascariensis_, L., Cuv.) 28

WALKER, FRANCIS, Esq., F.L.S. Catalogue of the Dipterous Insects collected at Makessar, in Celebes, by Mr. A. R. Wallace, with Descriptions of New Species 90

WALLACE, A. R., Esq. On the Zoological Geography of the Malay Archipelago 172

INDEX 185

JOURNAL OF THE PROCEEDINGS

OF THE

LINNEAN SOCIETY OF LONDON.

On the dermal armour of _Jacare_ and _Caiman_, with notes on the Specific and Generic Characters of recent _Crocodilia_. By T. H. HUXLEY, Esq., F.R.S., F.L.S., Prof. of Nat. History, Gov. School of Mines.

[Read Feb. 17th, 1859.]

In the course of a recent investigation into the nature of the singular extinct reptile, _Stagonolepis_, I was led to inquire somewhat minutely into the character of the exoskeleton, or dermal armour, of the existing _Crocodilia_. To my surprise, I found that very little detailed information on the subject was to be obtained from the standard repertories of Comparative Anatomy, or even from the special monographs on Crocodilian structure and classification; but I was still more astonished to discover, among whole genera of recent _Crocodilia_, an exoskeleton possessed of characters such as have been universally supposed to be peculiar to long extinct forms of the order, and whose existence in any recent species has hitherto, so far as I can ascertain, been completely overlooked.

The attempt to discover the limits within which this remarkable exoskeleton is to be found, led me to look, more critically than I had previously done, into the arrangement and specific characterization of the recent _Crocodilia_. I have thereby arrived at results which, imperfect as they are, may be of service by leading others to inquire into the exact characters of species not at present within my reach; and I therefore propose to preface my account of the peculiarities of the exoskeleton in two of the genera of recent Crocodiles with some remarks on the classification of the group, and with a few notes upon the characters of the species and the limits of the genera.

Everyone is acquainted with the great improvement effected in this branch of Herpetology by Cuvier, who divided the Crocodiles, which he regarded as constituting only a single genus, into the three subgenera _Alligatores_, _Crocodili_, and _Longirostres_. Subsequent writers have admitted these highly natural subdivisions; but there has been a constant tendency to raise their rank. The genus _Crocodilus_ has become the order _Crocodilia_; the subgenera _Alligatores_, &c., have been elevated into families; Dr. Gray has shown that the _Alligatores_ must be divided into three genera, and that there are at least two genera of _Crocodili_; and, while one of Cuvier's species of _Longirostres_ has been suppressed, the group is very generally retained with a changed name (_Gavialis_), a very important addition having been made to it in the _Crocodilus Schlegelii_ of Müller and Schlegel.

Unless the considerable materials contained in the British Museum, the Hunterian collection, the collection of Dr. Grant, and the Christchurch Museum at Oxford had been freely placed at my disposal, I should have been wholly unable to acquire the information contained in the following pages. It is only right, therefore, that I should take this opportunity of offering my thanks to my friends Dr. Gray, Prof. Quekett, Dr. Grant, and Dr. Rolleston for the many facilities they have liberally afforded me.

The recent species of the order _Crocodilia_ are divisible into three families, which correspond with the original subgenera of Cuvier, and may be termed the _Alligatoridæ_, the _Crocodilidæ_, and the _Gavialidæ_.

I. In the ALLIGATORIDÆ the teeth are strong and unequal, and the posterior ones differ greatly in shape from the anterior. The anterior pair of mandibular teeth, and the fourth pair (or the so-called canines) are received into pits in the margins of the premaxilla and maxilla; while the mandibular teeth behind these pass inside, and not between, the maxillary teeth. The mandibular symphysis does not extend back beyond the level of the fifth tooth, and often not nearly so far. The line of the premaxillo-maxillary suture on the palate is straight, or convex forwards. The wide posterior nares look downwards, and are situated forwards on the palate.

This family embraces three genera, readily distinguishable by osteological characters--_Alligator_, _Caiman_, and _Jacare_.

Genus 1. ALLIGATOR.

Dental formula, 20-20/20-20. 9th maxillary tooth the largest of its series. The snout is very broad, flattened, and rounded at the end. There is an indistinct longitudinal interorbital ridge; and there are two short ridges along the line of junction of the prefrontal and lachrymal bones. The aperture of the external nares is divided into two parts, by the prolongation forwards of the nasal bones. The supra-temporal fossæ are well-marked and open, though not large. The vomers do not appear in the palate. The feet are well webbed. The dorsal bony scutes are not articulated together; and there are no ventral scutes.

This genus contains only one species, the well-known _Alligator Mississipiensis_, or _lucius_, which is exclusively North American.

Cuvier (Oss. Foss. ed. 4. vol. ix. p. 211) gives the appearance of the vomer in the palate as a general character of the _Alligatores_; but this bone is not visible in the palate of any of those _Alligatores_ which Cuvier would have referred to his _A. lucius_ or _A. palpebrosus_, and which form the genera _Alligator_ and _Caiman_ as here defined. The vomers are in fact as slender and delicate as in the Crocodile, and extend only between the level of the tenth maxillary tooth anteriorly and the descending processes of the prefrontal posteriorly.

What may be called the median nares, or the arch formed by the postero-lateral part of the vomer and the anterior and superior lamina of the palatine bone on each side (which would constitute the posterior boundary of the posterior nares, if the palatine and pterygoid bones gave off no inferior or palatine processes), are situated nearly on a level with the twelfth tooth, or with the palato-maxillary suture.

Genus 2. CAIMAN.

Dental formula 20-20/22-22 (Natterer). The face is without median or transverse ridges, but it is sharply angulated along a line which extends from the orbit forwards along the sides of the snout. The anterior nasal aperture is undivided in the dry skull. The vomers do not appear in the palate. The supra-temporal fossæ are obliterated, the circumjacent bones uniting over them. The webs of the feet are rudimentary. The dorsal scutes are articulated together by lateral sutures and anterior and posterior facets; and there is a ventral shield, consisting of similarly articulated scutes.

Natterer[1] has described three species of _Caiman_--_C. palpebrosus_, _C. trigonatus_, and _C. gibbiceps_. The Caimans abound chiefly in tropical South America; but they are found as far north as Mexico, a specimen of _C. palpebrosus_ in Dr. Grant's collection coming from that country.

Genus 3. JACARE.

The snout is broad, and rounded at the end[2]. Each prefrontal bone is traversed close to its anterior extremity by the ends of a strong transverse ridge, which then curve round and pass forwards on the lachrymal and maxillary bones, to subside opposite the ninth tooth. The anterior nasal aperture is not divided by bone. The vomers, separated by a longitudinal suture, appear in the palate between the premaxillaries and the palatine plates of the maxillaries. The temporal fossæ, though not large, are open. The webs of the feet are small. The dorsal scutes are articulated together, as in the preceding genus; and there are similarly-articulated ventral scutes. There are 18-20 teeth on each side, above and below; and the fourth tooth in the upper jaw is the largest. The mandibular symphysis extends back nearly to the fifth tooth.

In a skull of _Jacare_ (_fissipes?_), 19 inches long, in the British Museum, I find that part of the vomer which is visible in the palate to be a rhomboidal plate, somewhat truncated anteriorly, and rather more than 1-1/2 inch long and 1 inch wide. Its anterior end comes within 3/8ths of an inch of the posterior margin of the anterior palatal foramen. Its posterior margin reaches to the level of the eighth tooth. The visible portion of each vomer is only its anterior end, which forms a thick and solid wedge-shaped plate, broader in front than behind, and articulating by a rough anterior and outer face with the premaxilla, by an obliquely ridged posterior and outer face with the maxilla, and by its internal face with its fellow. Its upper, rounded surface projects but little into the nasal passage. 2-1/4 inches behind its anterior end, the posterior and upper extremity of the vomer passes into a thin and narrow plate of bone, whose plane is at first inclined at an angle of 45° to that of the anterior part of the bone, but gradually becomes vertical; as it does so it deepens, until, 3 inches behind the anterior extremity, the vomer is a thin vertical plate of bone, 5/8ths of an inch deep, which articulates below with the palatine plate of the maxilla, and, about 1 inch behind this, with the palatine plate of the palatine bone. The upper edge of this plate nowhere extends to one-third of the height of the nasal chamber. It gives off a horizontal process outwards, which, gradually increasing in width, inclines downwards until it comes into contact, first, with the inner surface of the maxilla, and, 3/4ths of an inch behind this, with the nasal plate of the palatine bone. In front of its junction with the maxilla, the horizontal plate of the vomer presents a long free edge, concave externally; and this bounds the median nares internally and posteriorly. Throughout its junction with the maxilla, the horizontal plate is parallel-sided; but after it joins the palatine bone, it gradually narrows posteriorly, in consequence of the gradual increase in width of the palatine, and ends almost in a point, 6-1/4 inches behind its anterior end. The posterior edge of the vertical plate is extremely thin, and 7/8ths of an inch deep. It articulates with the anterior end of the vertical plate of the pterygoid, while the straight inferior edge articulates throughout with the palatine plate of the palatine bone. The vomers terminate midway between the median nares and the descending process of the prefrontal. The median nares are bounded entirely by the vomer and the maxilla. They correspond with the nasal face of the palato-maxillary suture, but are rather behind its palatine face, and they are about on a level with the interval between the tenth and eleventh teeth. If the anterior edge of the palatine bone bounded them, they would be a little behind the twelfth tooth. The posterior nares, 2-1/8 inches wide, by 7/8ths of an inch long, look altogether downwards, are completely divided by a bony septum, and have the form of a rhomboid with its narrowest side posterior. They are surrounded by a strong raised ridge, incomplete only at the anterior and outer angles of the rhomboid.

Five species of _Jacare_ are enumerated by Natterer--_J. fissipes_, _J. sclerops_, _J. nigra_, _J. punctulata_, and _J. vallifrons_. They have met with only in South America.

[1] "Beitrag zur näheren Kenntniss der Sudamerikanischen Alligatoren," 'Annalen des Wiener Mus.,' Band i.

[2] According to Natterer, the dental formula of _J. nigra_ and _J. fissipes_ is 18-18/18-18, of _J. sclerops_ 19-19/20-20, of _J. callifrons_ and _J. punctulata_ 20-20/18-18.

* * * * *

II. In the family of the CROCODILIDÆ the teeth are usually strong and very unequal in size, and there is always a considerable difference between the anterior and the posterior teeth. The two anterior mandibular teeth are received into pits in the premaxilla; but the canines pass into grooves (which may be converted into fossæ) situated at the junction of the premaxilla and maxilla. The other mandibular teeth are received between the maxillary teeth. The symphysis of the lower jaw does not extend beyond the level of the seventh or the eighth mandibular tooth. The premaxillo-maxillary suture may be either straight or strongly convex backwards. The divided vomers do not appear in the palate. The posterior nares look more or less backwards, and are transversely elongated. The supra-temporal fossæ are always open, and the feet are distinctly webbed. The dorsal scutes are not articulated; and there are no ventral scutes.

Two genera, _Crocodilus_ and _Mecistops_, are distinguishable in this family.

Genus 4. CROCODILUS.

The teeth are always strong and very unequal, the strongest in the upper jaw being the tenth. The mandibular symphysis does not extend beyond the level of the sixth tooth. There are usually six cervical scutes, in two rows, or forming a rhomb, and separated by a distinct interval from the tergal scutes. There are 18 or 19 teeth above, and 15 below, on each side.

1. _Crocodilus vulgaris._

As Cuvier has remarked, it is extremely difficult to find good distinctive characters for all the species of this genus. My first difficulty was to ascertain the precise characters of that species which has been misnamed _vulgaris_, inasmuch as I could find neither in the British Museum, nor in the Museum of the Royal College of Surgeons, any _authentic_ skeleton or skull of this, the so-called Nilotic Crocodile. This difficulty subsisted up to the time that the chief statements contained in the present essay were laid before the Linnean Society; but since then I have been enabled, by Dr. Gray's permission, to examine the skull of a small stuffed specimen, brought to this country from Egypt by Sir Gardner Wilkinson, and to study the splendid entire skeleton of a _Crocodilus vulgaris_ in the Christchurch Museum at Oxford, presented to that Institution by the gentlemen who shot it on the Nile, and set up with great care under the auspices of my friend Dr. Rolleston, Lee's Reader in Anatomy and Curator of the Museum. Fortunately the entire skin has been preserved; so that this is the most complete record of the hard parts of any individual crocodile with which I am acquainted, besides being, so far as I am aware, the only authentic entire skeleton of _Crocodilus vulgaris_ in this country. I subjoin the chief points of interest which I noted in my brief examination of this valuable specimen:--

Inches.

The total length of the skeleton is 114 " " " skull 16 Between the outer edges of the posterior ends of the quadrate bones 8-3/4 From the snout to the middle of the canine notch 2-3/4 Transverse diameter of snout opposite 10th tooth 4-7/8 Long axis of orbit 2-1/4 Short axis of orbit 1-5/8 Interorbital space opposite the middle of the orbit 1-3/4 Anterior edge of the orbit from end of snout 10-1/2 Syncipital[3] area in length, about 2-1/2 " " in breadth anteriorly 3-3/4 " " " posteriorly 4 Supra-temporal fossæ, wide 7/8 " " long 1-1/8 Least width of parietal 7/16 Total length of mandible 20-1/2 Its greatest depth 3 Length of cervical region (or anterior 8 vertebræ) 10-1/2 " dorso-lumbar region 27 " sacral " 3-3/4 Length of humerus 7-1/2 " ulna 5-1/4 " fore foot, extreme length 6 " femur 8-1/2 " tibia 6 " hind foot, extreme length 9-1/4

From the above measurements it will be seen that the skull is somewhat slender. Behind the canine groove it widens to the tenth tooth, which is 5-3/4 inches behind the end of the snout. It retains about the same diameter to the twelfth tooth, and then slowly widens again,--a sudden increase in size, to the extent of half-an-inch, taking place opposite the posterior margin of the orbit, owing to the flanging-out of the jugal. On the whole, however, there is a slow and even increase in breadth, from the canine groove to the ends of the ossa quadrata. The nasal aperture is pyriform, its wider end being forwards, and its narrow posterior extremity, into which the pointed ends of the nasal bones project, attaining the level of the first tooth behind the canine groove.

[3] By this term I denote that squarish flat area bounded by the postfrontal and squamosal bones laterally, by the occiput posteriorly, and by a line joining the outer angles of the postfrontals anteriorly.

On the left side there is only a pit for the reception of the anterior mandibular tooth, while on the right side this pit is converted into a complete foramen. On the upper face of the skull, the premaxillo-maxillary suture runs vertically upwards through the canine groove, and then passes obliquely backwards to a point 5 inches behind the end of the snout. The anterior part of this suture lies in a strong ridge, which is continued downwards and forwards on the premaxilla to the level of the fifth tooth, a groove separating it from the margin of the nasal aperture. Posteriorly this ridge dies away, but a curved irregular elevation, convex inwards, arises opposite the tenth tooth. It is wholly confined to the maxilla, not extending on to the nasals.

There is a distinct, rough, irregular elevation, bounded on its outer side by a sharp groove, which extends back to the orbit, on the lachrymal bone. The profile of the skull is convex as far as the posterior boundary of the nostril, and very slightly concave from that point as far as the twelfth tooth. It then passes back as a straight, slightly ascending line, only interrupted by the lachrymal ridge, to the margin of the occiput. The inferior margin of the maxilla is convex downwards as far as the canine groove, whose lower end is indicated by a deep sinuation. It then becomes convex again, the crown of the curve being at the ninth and tenth teeth, and its posterior end sweeping into a concavity whose summit is at the twelfth tooth. Behind this the edge of the maxilla is only slightly convex. The inferior contour of the jugal bone is very concave; but the articular end of the quadrate bone descends to the level of the edge of the ninth alveolus.

The orbits have a sort of heart-shape, their apices being turned forwards, and their more convex sides inwards.

The supra-temporal fossæ are half-moon-shaped, their straight sides being external and so inclined that, if prolonged, they would decussate upon a line joining the anterior margins of the orbits.

On the palatine surface of the skull, the premaxillo-maxillary suture runs backwards from the canine groove, as far as the level of the middle of the second alveolus behind the groove (or that of the seventh tooth), which point it reaches at about the junction of the middle with the inner third of the palatine plate of the maxilla. The suture then turns abruptly forwards until it reaches the level of the anterior margin of the alveolus of the sixth tooth, when it bends suddenly inwards to meet its fellow. The whole suture, therefore, has the form of a W. The vomers are completely hidden.

The posterior nares look downwards and backwards; their aperture is, from the incompleteness of the septum, single, and has a transversely elongated crescentic form. It measures 1-1/8 inch in width by 3/8ths antero-posteriorly. The basi-sphenoid is seen for about 1/8th of an inch on the base of the skull behind it, bounding the sides of the eustachian tube. The dental formula is 18-18/15-15. The fourth and tenth teeth are largest in the upper jaw, the first and fourth in the lower. The eight posterior teeth on each side in the upper jaw, and the five posterior in the lower, have a marked constriction between the short crown and the fang of the tooth. There are deep interdental pits for the reception of the mandibular teeth between the third and fourth, and fourth and fifth teeth above, and between the succeeding teeth from the sixth to the thirteenth.

The hyoidean cornua are very strong curved bones, the chord of whose arc measures 3-1/2 inches. They are concave inwards, convex outwards, concave posteriorly, convex anteriorly; they are flattened from side to side below, but they end above in subcylindrical styloid extremities.

In the ninth vertebra the neurocentral suture passes just above the base of the parapophysis; it traverses the parapophysis in the tenth and eleventh vertebræ, while in the twelfth the parapophysis suddenly rises to the root of the diapophysis, and the suture lies far below it. The centra of the dorsal vertebræ, as far as the thirteenth inclusive, have hypapophyses. The diapophyses of the ninth vertebra pass almost horizontally outwards, but are a good deal inclined backwards. In the succeeding vertebræ up to the fourteenth or fifteenth, the diapophyses are, in addition, inclined upwards, the upward inclination being most marked in the tenth, eleventh and twelfth vertebræ. From the fifteenth vertebra onwards, the transverse processes pass almost directly outwards, without either upward or backward inclination. The span of the transverse processes is greatest in the eighteenth and nineteenth vertebræ, in which the distance between the extremities of these processes is 7-1/4 inches, a length about equal to that of the longest vertebral rib.