356 SIB C. ELIOT OX NUBIBRANCHS' [Dec, 1^ 



the gromp, is bound to consider the vaslue of the existing generic- 

 distinctions. The five subfamilies are divided into abovit 30 

 genera all created by the great master of the JSTudibranchiata, 

 Prof. Bergh, and several of them consisting of a single species. 

 He himself observes (on Thordisa in Sempei-'s ' Reisen ' *, xv, 

 p. 666) that the definitions of many of these genera seem to be 

 too pi-ecise, and as new forms are discovered the old divisions are 

 found to melt away. The discoverer of a new form often finds^ 

 that it does not accurately fit in to any of the existing genera, 

 and must ask himself whether he should create a new genus or 

 enlarge the definition. I have Jittle doubt that in most cases 

 the latter is the preferable course. If animals are not divided by 

 natural differences, there is no object in emphasising the im- 

 portance of minute peculiarities. If Chromodoris is fillowed to 

 consist of 100 species showing a considerable range of variation, 

 including the presence or absence of median teeth, there seems to> 

 be a want of proportion in splitting up the other Oryptobranchiata 

 into so many genera. 



The genus Staurodoi-is offers a good example of the difficulty 

 of classifying new forms. Taken by itself, the typical species 

 >S'^. verrticosa is remarkably well characterised in both the scien- 

 tific and popular sense. Anyone could recognise it at first sight. 

 The back is covered with club-like tubercles, the rhinophorial and 

 branchial pockets are protected by similar tubercles which act 

 as valves, and the branchiae are simply pinnate. On the other 

 hand, ^S"^. pseitdoverrucosa (von Ihering) has no tiibercles on the 

 bi'anchial pocket and has bijiinnate branchiae. Bergh also refers to 

 this genus the Doris pustidosa of Abraham, which has bipinnate 

 branchife and small, but apparently not valve-like, tubercles. I 

 have specimens from the Indian Ocean which have the dorsal 

 surface tuberciilate and the following additional characteristics : — ■ 

 A . has the rhinophores arising among tubercles and simply pinnate 

 branchiae, but no tubercles on the branchial pocket {Staurodorisi 

 pecten). B. has five pinnate gills, the anterior margin of the foot 

 entire, and small tubercles set on the edges of the gill-pocket and 

 partly closing it {Staurodoris ccdva). C. has tubercles I'ound the 

 rhinophores, none on the branchial pocket, and thin bipinnate 

 branchiae {Archidoris africcma). D. has tubercles on the rhino- 

 phore pockets but not around the branchial opening, and ti'i- 

 pinnate gills {Archidoris minor). Of these, I think we must admit 

 A . and B. to be Staurodoris, if we accept St. pseudoverrucosa. 

 But Archidoris kerguelensis, A. austrmlis, A. ruhescens, A. incerta, 

 and A . 7iyctea are all described by Bergh as having tubercles on 

 the edge of the branchial and rhinophorial pockets, and must 

 come very neax the less typical members of Staurodoris. It is 

 hard therefore to say whether C. should be classed as Staurodoris^ 

 or Archidoris. There seems to be a complete series of links 

 between the two genera, and, this being so, we must either unite 



* The letters S. R. in this paper refer to Prof. Bergrh's " Malacologi.'iche Unter- 

 sachmigen," pubJishecl in 'Eeisen im Auchipel der Pliilippinen,' von Dr. C. Semper. 



