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Show 1904.J FROM EAST AFRICA AND ZANZIBAR. 87 The buccal mass is rather large, the radula fragile, with a wide rhachis. There are 21 rows in all, some of the longest of which contain 24 teeth on each side. The first tooth (fig. 3 a) is larger than the rest, and projects into the rhachis ; it is slightly bent, but hardly hamate. All the first teeth are similar and regular in shape. The base is somewhat wavy and as if hollowed out. The other teeth are awl-shaped, with an irregular and somewhat bifid base (fig. 3 c). The liver is yellowish grey and not very large. In front of it are two hermaphrodite glands, much as in T. coccinea, but smaller. The verge is armed with numerous short thorns of very varying shape. I think this animal is probably Kelaart's T. ceylonica, for which the genus was founded, and which appears not to have been described since; but it is difficult to be certain of the identification, as he gives no information respecting the radula. The form and colour agree well, including the red lines on the branchiae and round the foot. The chief difference is that whereas his specimen has 15-16 pure white branchiae " set round a large disk," mine had 12 yellow branchiae set in a circle open behind. But his specimen was nearly twice the size of mine, and probably the larger individuals develop extra plumes which close up the posterior gap. On the other hand, both specimens agreed in having rather large feathery branchiae, an unusual character in the genus. Kelaart says " they resemble a small tuft of marabout feathers." T r e v e l y a n a crocea B. (Plate III. fig 4 .) [Bergh, in Semper's Reisen, xvi. 2, p. 850, figs.] More than 100 specimens from the East and West Coasts of Zanzibar, where it is one of the commonest littoral molluscs at certain seasons. Mr. Crossland, who collected them, informs me that this form provided a most striking case of the migration of molluscs in flocks to shallow water for the deposition of spawn. But few specimens were collected before a certain period of a few days' duration, when the sand of Chuaka Bay just below low-tide mark was occupied by astonishing numbers of these delicate little nudibranchs. These were not washed up by accident, but were all actively crawling on the sand among the weeds &c. Many were in coitu, and when placed in basins of sea-water most of the specimens were soon engaged in copulation or the deposition of yellow egg-ribbons. By-and-by the swarm disappeared to some unknown permanent habitat. If this were in the deeper channels of the bay (1 to 2 fathoms deep at low tide) they must have been found there by dredging. As this was not the case, it seems most probable that the migrations of these tiny animals extend to and from the deep sea three or more miles away. An almost equally conspicuous swarm was formed by individuals of Melibe fimbriata, and other species (e. g. Ceratosoma cornigerum, Chromodoris spp., and Pleurobranchus delicatus) appeared occasionally for a few days in considerable though |