1903. J FROM EAST AFRICA AXD ZANZIBAR. 357 



the species in question, or draw an arbitrary dividing line. In 

 the latter case, I think we must say tliat the typical iStaurodoris 

 has simply pinnate branchije and valve-like tubercles closing the 

 rhinophoriiil and branchial pockets. One or other of these 

 features may be absent or obscure in a species which otherwise 

 possesses the generic characteristics ; but when both are absent, 

 as in C, the animal, I think, must be referred to Archidoris. 

 Again, Skoarodoris pseiuloverrucosa has the dorsal tubercles some- 

 times counected by ridges, and the same phenomenon is found 

 in Garstang's Boris maculata (which appeal's to be a >Staurodoris), 

 and, sporadically, in the true *S'^. verrucosa. But, as will be seen 

 from a species described below, Ualgerda wasinensis, this chai-acter 

 brings Staurodoins very near to Halgerda. 



It will be well to examine the value of the chief points by 

 Avhich the subfamilies and genera under consideration can be 

 differentiated. They are as follows : — ■ 



{a) The dorsal surface and general texture. The back is rarely 

 quite smooth, as it is in Chromodoris\ Halgerda and Aatero)iokis 

 have the skin smooth but raised into ridges or lumps. As a rule, 

 the surface is covered with pi-ojections which may be either 

 minute granulations (^Platyduris, Discodoris, &c.), papillae [I'hor- 

 disa, &G.), tubercles {Archidoi-is, &c.), clavate tubercles or warts 

 [Staiirodoris), compound tubercles [Trippa, Fracassa). There is 

 sometimes a ridge down the centre of the back. Some genera, 

 notably Platydoris, are exceedingly hard ; others, such as Tripjxi, 

 are so soft as to be almost gelatinous. On the whole, these 

 external characters of the skin and texture form a fairly good 

 indication of relationship. Platydoris^ in which I should be 

 disposed to include Hoplodoris, forms a distinct natural group, 

 and the warty or tuberculate forms {^Archidoris, Staarodoris) also 

 hang together*. 



(6) Rhinophores and branchiae; Neither the rhinophores 

 themselves, nor the pockets into which they are retractile, seem 

 to offer good generic characters, though they may often serve to 

 distinguish species. But even within a species there may be 

 variety : Archidoris tuhercidata has the lims of the rhinophore 

 pocket sometimes smooth and sometimes tuberculate. 



The branchiae also are disappointing as a means of classification. 

 For instance, it does not seem possible to vinite Staurodoris with 

 the other genera having simply pinnate branchiie (Chromodoris, 

 Casella, Ceratosoma, Sphcerodoris, Halla, Thorunna, Eostanga), 

 and these simple branchiae often show a tendency to divide at 

 the tip and become, strictly speaking, bipinnate. Similarly, we 

 cannot bring together bipinnate forms and oppose them to the 

 tripinnate. Perhaps the distinction between ample and scanty 

 branchiae will prove to be of generic importance. The branchial 

 pocket is of various shapes : round, crenulate, or stellate. However, 



* I find it hard to agree with Prof. Bergh's criticism of his own family Arclii- 

 dorididae that it will prove " gauz unhaltbar und kiinstlich." With the except iou 

 of FeJtodoris the other forms seem to hang well together. 



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