1904,] FROM EAST AFRICA AND ZAXZIRAR. 381 



nearly all Lave a labial armatui-e, and all* have teeth nioi-e or less 

 differentiated. I confess that 1 am afraid of attaching too much 

 importance to the radula : a case like Aldisa, where a Dorid with 

 otherAvise ordinary characters has a unique dentition, certainly 

 shows that the teeth may vary without any corresponding change 

 in other characters ; but in the genera here grouped together it 

 will be found that the buccal characters are u^sually accompanied 

 by some other feature which allies them to Chromodoris. such as 

 simply pinnate Ijranchife or a long narrow shape. It may be said 

 that the teeth of Dorids are never really uniform, and in the 

 genera described in my previous paper are often denticulate at 

 the outer end of the row. This is true, but the outei'most teeth 

 are less well developed and more exposed than the others. They 

 therefore have a natural tendency for purely mechanical reasons 

 to become smaller and more irregular, and a particular form of 

 this irregularity, due perhaps to some peculiarity of textui'e, is 

 seen when they split up and become jagged or denticulate. But 

 no such mechanical explanation will account for the innermost 

 teeth being larger and more elaborately formed than the i-est. 

 Also this peculiarity is confined to certain genera, whereas the 

 irregularity of the outermost teeth is general among the Ciypto- 

 branchiates and as noticeable in Chromodoris as elsewhere. 



Casella and Ceratosoma are clearly closely allied to Chromodoris, 

 the former being perhaps not really a separate genus. Thorunna 

 is practically Chromodoris without a labial armature. Ajihelodoris 

 has an elongate shape and narrow mantle-edge, but tripinnate 

 branchiae and no labial armature. It seems, however, to be allied 

 to Chromodoris by the presence of an accessory denticle on the 

 innermost teeth. The remaining genera ai'e of more or less oval 

 shape, with a, fairly wide mantle-margin, and papillte or tubercles 

 on the back, peculiarities which are found in some species of 

 Chromodoris. Sphcerodoris has simply pinnate branchife and a 

 radula which, though peculiar, is essentially of the Chromodoris- 

 type. Orodoris. which Bergh associates with Sphcerodoris and 

 Miamira, has the median pai't of the I'adula much as in Chromo- 

 doris. Hallaf mM\ Bostavga ai'e allied to Chromodoris by their 

 simply-pinnate branchife as well as by their buccal parts : indeed, 

 the former apjjears to me almost an aberrant Chromodorid akin to 

 such forms as Chr. sykesi described below. In Rostanga the 

 Mediterranean species perspicillata has denticulate inner teeth : 

 in coccinea they ai-e mei-ely bifid. The buccal parts of Tyrinnrx 

 and Cadlina strongly i-esemble those of Ckr. scabriusciila. whicli 

 has also a somewhat oval form and tuberculate back. I somewhat 

 doubtfully refer Audura to the same group, in virtue of its radula. 

 This position is somewhat supported by its smooth skin and 

 scanty bipinnate branchiae, but the structure of the foot suggests 

 other affinities. 



* Except the very anomalous Jliamira, which Bergh regards as allied to Sphcero- 

 doris and Orodoris. 

 t See note § on p. 380. 



