i. 108;

on the hatching of the eggs in the mouths and branchial cavities of male fishes, i. 210, ii. 20.

X.

XENARCHUS, on the Cicadae, i. 350.

_Xenorhynchus_, sexual difference in the colour of the eyes in, ii. 129.

_Xiphophorus Hellerii_, peculiar anal fin of the male, ii. 9, 10.

_Xylocopa_, difference of the sexes in, i. 366.

Y.

YARRELL, W., on the habits of the Cyprinidae, i. 309; on _Raia clavata_, ii. 2; on the characters of the male salmon during the breeding season,