400 SIR c. ELIOT ON xuDiBRAxcHS [Mar. 1, 



space behind. They are 24 in number : those in front are fairly 

 large, but the size diminishes backwards, and those in the spirals 

 are extremely small. The head and anterior poi-tion of the foot 

 are much retracted, but the latter was appai'ently round and 

 grooved in life. 



The mouth leads into an unusually large and spacious cavity, 

 but the buccal mass is very small, the radula minute, and the 

 oesophagus extremely narrow. The labial armature is small but 

 strong, with rough projecting teeth ; the elements are small, 

 yellowish, bent rods, mostly bifid. JN'o rhachidian thickenings are 

 visible ; the innermost teeth have three denticles on the inner 

 and about four on the outer side. The remainder have mostly 

 five on the outer side only. The number of denticles increases 

 towards the outside of each row, but the outermost teeth are 

 smooth. The teeth are very small, ci'owded, and extremely 

 numerous. 



This specimen corresponds with previous desciiptions of C. atro- 

 tnarginata, except that there are no thickenings on the rhachis 

 of the radula and that the gills are much more numerous than in 

 the specimens previously described. There seems to be some doubt 

 on this point (see Bergli, Mus. Godefii'. 1. c), but the arrangement 

 in the pi-esent specimen is perfectly clear. Casella cincta fi'om 

 Maxu^tius has 22 gills (Bergh, S. R. xvi. 2, p. 839), but presents 

 diiferences in the coloration and buccal parts. 



Genus Ceratosoma, Adams & Reeve. 



This genus is rendered unique among Nu.dibranchs by its extra- 

 ordinary shape, but in its essential characters it is closely allied 

 to Chromodo7-is. Indeed, if one looks at one of the high, stout 

 Chromodorids (e. g. the figure of C. semperi in S. R. Heft xi. pi. Iv. 

 fig. 2), it will be seen that one has only to somewhat prolong the 

 tail and to thicken and develop the mantle-edge in order to obtain 

 the characteristic shape of Ceratosoma. The large strong radula 

 is lilve that of Chromodoris, but the denticles are minute and 

 inconspicuous. The branchiae are much divided. Bergh i^ecognises 

 nine species, but I have only seen the descriptions of those 

 examined by himself {coi-nigerum^ gracillimtiin, trilohatum, orna- 

 tum, pohjomma). In Zanzibar I have inspected more than forty 

 specimens which are apparently referable to one species, and are 

 connected together by numeroxTS gradations in colour and shape, 

 though the extreme foi-ms look remarkably difierent. As the five 

 species mentioned above are distinguished by theii- external 

 characters only, and offer no certain differences in the dentition or 

 other organs, I am inclined to think they are merely varieties and 

 that there is only one real species. It is to be noted, however, 

 that though many of my specimens resembled the figure of 

 Cey^atosoma gracillimtim (S. R. pi. xxv. fig. ^) the border was never 

 red as there depicted, but always violet, and in no case did ocelli 

 occur as in C, polyo7)ima. 



