550 SIR CHARLES ELIOT. 



that when the gills are contracted it almost covers the branchial lamellae, like the valve 

 in Notodoris. No tentacles were discernible : the inner lip is brown, and bears a weak 

 armature of small rods: the formula of the radula appears to be 11+1 + 1 + 1 + 11. The 

 central tooth is squarish : its front edge is turned upwards, and bears four or five denticles. 

 The first lateral is large and sickle-shaped: the rest squarish without hooks, and decreasing 

 in size outwards. Blood-gland large. The hermaphrodite gland spread over the liver. Verge 

 armed with small hooks. 



The tj'pical Nembrotha nigerrima appears to be black, with bluish-green spots, red gills, 

 and a red mantle border. Several species of Nembrotha which I have preserved in spirits 

 have kept their colour well, and I do not think it likely that the ground colour of the 

 present specimen was ever black. I am very doubtful if this individual should be referred 

 to N. nigerrima, as both its shape and coloration seem different, but I cannot formulate any 

 separate specific characters. 



Fam. Dorididae cryptobranchiatae. 



The cryptobranchiate Dorids are characterized by the possession of a distinct and perma- 

 nent dorsal pocket, into which the branchiae can be entirely withdrawn. The rhinophores 

 are invariably perfoliate and retractile. There is never a buccal gizzard. A labial armature 

 is present or absent. The radula is broad, and the teeth either uniform or only slightly 

 differentiated. A central tooth is rare. 



In number of species this is the richest family of all the Nudibranchiata. Though 

 cosmopolitan in distribution it is particularly abundant in the Tropics. 



Gen. Chromodoris A. and H.' 



The form of this genus is generally high, narrow, and limaciform, the mantle being 

 somewhat small at the sides, but expanding into a fairly ample frontal and caudal veil. 

 The coloration is brilliant. The foot usually projects behind the mantle. The branchiae 

 are simply pinnate, but are sometimes bifid and vary considerably in their arrangement. 

 The tentacles are retractile. The labial disk has a strong armature of minute hooks. The 

 rhachis of the radula is either naked or bears thickenings, very rarely true teeth. The laterals 

 are numerous and hamate : the first is denticulate on both sides, those which succeed it 

 on the external sides only, the outermost at the extremity only. 



Chromodoris is the largest genus of the Cryptobranchiatae, comprising over a hundred 

 species. Many of these resemble one another closely in structure, but some show remarkable 

 variations such as Chr. scahriuscula, which has a hard tuberculate back and rhachidian teeth, 

 peculiarities which almost entitle it to generic rank. Also the shape is somewhat variable. 

 Typically, it is as described above, but some species are flatter with an ample mantle margin, 

 and present a quite different appearance. Many tropical Chromodorids have considerable powers 

 of altering their form, and alternate between a high narrow condition and a flat condition 



1 Bergh in S. E. xi. Supp. Heft i., Hefte xv., xvi., xvii. Challeiiger Report on Nudibranchiata, 1884. von Jhering, 



Bergh, " Neue Nacktschnecken der SiiJsee," Journal des Mus. " Beit, zur Kennt. Nudibr. Mittelmeeres," Mai. Blotter, N. F. 



Go(i<:/froi/, Heft VIII. 1875 and Heft XIV. 1878. " Untersuchung Bd. ii. 1880. CoUiugwood, On some Neic Nudibr. Mollmca 



der Chr. elegans u. Villafranca," Mai. Blatter, xxxv. 1878. from the Eastern Seas, 1878. 



