NUDIBRANCHIATA. 547 



owing to the action of alcohol, but the following characters seem certain and sufficient 

 to establish a new species. The mantle is extremely ample and much crinkled, recalling 

 in this respect Tridachia; when extended from the body, the free edge measures 3'4 cms. 

 Over the head are three digitate processes, which are not due to undulations but are 

 distinct and permanent projections from the mantle edge. The rhinophores are not much 

 bent back. The tentacles are almost arborescent ; they arise from short stalks, and are 

 deeply indented and subdivided. The buccal parts, nervous system, and reproductive organs 

 are as usual in the genus. The radula and labial armature are strong and reddish-brown 

 in colour. Both the head and the branchiae are withdrawn to an unusual degree into the 

 body. The latter are partly covered by an anterior flap of skin and are crowded together, 

 so that the usual division into groups is not clear. The sections are however divided from 

 one another by eight membranous septa. If this arrangement could be considered with 

 certainty as structural it would afford an interesting link between the ordinary branchial 

 arrangement of Hexabranchus and that of the cryptobranchiate Dorids, but in view of the 

 generally wrinkled and contracted state of the specimen I do not think it safe to regard 

 this configuration as more than a distortion, and should define the species by the following 

 characters — mantle edge extremely ample with digitate processes over the head : tentacles 

 much subdivided and almost arborescent. But it must be remembered that specimens of 

 Hexabranchits which seem to be mere varieties exhibit great differences in the extent to 

 which the mantle and tentacles are developed. 



Fam. Dorididae phanerobranchiatae. 



A number of Dorids are conveniently grouped together as Phanerobranchiata, that is to 

 say, they have no distinct and permanent dorsal cavity into which the branchiae can be 

 retracted, though when touched the branchiae may contract so strongly as to almost dis- 

 appear. Bergh divides them into the Goniodorididae, which possess a buccal gizzard (ingluvies 

 buccalis), and the Polyceradae, which do not, an arrangement which brings together forms 

 of such different appearance as Lamellidoris and Ancula. It seems to me that it would 

 be more natural to subdivide the group into Polyceradae with limaciform bodies, sometimes 

 bearing appendages, and Pseudodorididae, flat Dorid-like forms. It would appear that in 

 other groups closely related genera may either possess or not possess this buccal crop. 

 Thus it is present in Placobranchus and Tridachia, but absent in Elysia. The Pseudodori- 

 didae seem to be confined mainly if not entirely to northern seas. 



The radula of the Phanerobranchiata is usually narrow and with differentiated teeth. 

 They show a greater variety of form than the Cryptobranchiata, but are far less numerous 

 in species. 



Gen. Notodoris B.' 



Body limaciform, with no clear distinction between the back and sides: hard, rough, 

 and rugose ; surface filled with spiculae. Frontal veil large. Rhinophores smooth, protected 

 by valves. Gills protected by a large valve, which is sometimes elaborately subdivided. No 

 labial armature. Radula without central tooth but with numerous hamate uniform laterals, 

 having a rudimentary secondary denticle below the main hook. 



' Bergh, " Neue Nacktschnecken d. Slidsee, iii." Journal d. Mus, Godeffroy, viii. 1875. 



70—2 



