360 SIR C. ELIOT OX NUDIBRANCES [DeC. 1, 



prostate is present in both Discodoris and Plaij/doris, which are 

 otherwise so distinct, and is absent in Archidoris but piesent in 

 Anisodoris, which are otherwise identical, (iii-) In many genera 

 is present an armature of the reprodvictive organs, that is, one 

 or many spines, hooks, or plates generally only on the male 

 blanch. The value of this feature, as estimated by the con- 

 comitance of other important characters, varies. In the families 

 of Doridop-sidfe and Phyllidiadse and in the well-maiked genus 

 Platydoris of the Ciyptobranchiata an ai-matiu-e is, so far as we 

 know, charactei'istic. On the other hand, we find two genera 

 like Dicmlida and Gai'gamella appai'ently identical but for its 

 piesence oi- absence. In the Aeolidiadse also a hook or spine is 

 pi-esent or absent in closely allied genera. It appeals to me that 

 such an armature is not sufficient to constitute generic rank 

 without other characters. 



( /') The othei- internal organs do not offer many features 

 which serve our purpose of classification. It does not appear 

 that we can unite the forms in which the stomach is enclosed 

 in the liver, or in Avhich there is only a single instead of a 

 double blood-gland, or in which the nervous system is very 

 concentrated. 



As a result of these considerations, I think that the most pro- 

 fitable way of classifying new Doi-ids of the group treated of here, 

 is to refer them when possible to the following genera taken in a 

 wide sense: — Archidoris, Discodoris, Thordisa, Trippa, Hcdgerda, 

 Kentrodoris, Platydoris, Asteronotus, and Sclerodoris (gen. n.). 

 No doubt, remarkable foi'ins have been and will be found which 

 require special genei'a for their accommodation, but the majority 

 of species seem to me to fall under one or other of the divisions 

 mentioned. 



Archidoris is distinguished by a fairly plump shape, broad foot, 

 and a waity or tuberculate back. No member of this group is 

 known to possess a labial armature, and a genital armature is 

 rare. The ladula generally consists of uniform, simply hamate 

 teeth : more I'ai'ely some or all are denticulate. I include in 

 this genus, in its wide sense at least, Anisodoris, Uomoiodoris, 

 and Artachceo. As mentioned above, though it is easy to define 

 the generic characters of a typical Staurodoris, the genus seems 

 to pass into Archidoris by a complete series of connecting links. 



Discodoris. — I should be inclined to extend this genus so as to 

 mean flat, oval animals, not haixl, with both foot and mantle- 

 brim fairly broad. Back granulate. A genital aimature is 

 usually absent ; a labial ai-matui'e is either pi-esent (Section 

 Discodoi'is) or absent (Section Peltodoris). 



Thordisa. — Flat, soft animals, much like Discodoris, but with 

 the back neither granulate nor wart}-, but covered with soft 

 pointed papillse. No member of this group is known to possess 

 a. well-developed lalnal aimature, though a rudimentaiy one is 

 found in Th, crosslandi, 

 [S] 



