364 Mr. W. Clark on the Littorinidse. 



of my position, that the spurious species belong to L. rudis, and 

 of course follow the habitudes implanted by nature in the parent. 

 It may be asked, does not the very important fact of the vivipa- 

 rous reproduction of L. rudis and its varieties indicate something 

 more than specific distinction ? I partook of this opinion, but 

 on consulting a naturalist of the highest authority, he informed 

 me, that in the lower classes, the fact of an animal being vivipa- 

 rous, without other circumstances, when its congener was ovo- 

 viviparous, did not constitute sufficient grounds for generic di- 

 stinction. The question is open, and I leave the solution of this 

 problem to those w^ho are better versed than myself in the my- 

 sterious laws of nature which relate to the genesis of the Mol- 

 lusca. 



I could adduce many more examples of various values, of the 

 sad confusion that has crept into and disfigured this highly in- 

 teresting department of natural history, from the introduction of 

 phantoms into our records, instead of soundly settled species. I 

 refrain, and rest for the present on the great examples I have ad- 

 duced in illustration of these observations, on the principle that 

 " omne majus in se minus continet.^^ If the preceding remarks 

 have the effect of causing greater circumspection in future in the 

 creation of species, the object I have had in view will be accom- 

 plished. 



I am. Gentlemen, your most obedient servant, 



William Clark. 



Postscript. — I take this opportunity to refer to some species 

 of Mollusca which have lately been mentioned in our records. 

 Having obtained fifty specimens of the Trochus pusillus of authors, 

 I am enabled beyond doubt to state, that it is the living proto- 

 type of the fossil Delphinula nitens of M. Philippi, tab. 25. ^^. 4, 

 and that the Skenea Cutleriana discovered by me is scarcely di- 

 stinguishable from M. Philippics Delphinula elegantula, also a 

 fossil, tab. 25. fig. 3 ; the only distinction is, that the spiral striae 

 of Skenea Cutleriana are twice as numerous as those of D. ele- 

 gantula ; this may arise from habitat, but I think the two distinct. 

 The Trochus exilis of Philippi has not the slightest approach to 

 S. Cutleriana. Whatever generic appellation may ultimately 

 be applied to the Skenea divisa of authors, the same must be- 

 long to the S. Cutleriana, as the character of the capillary strise 

 is precisely similar. They are not Trochi, and I believe the 

 Trochus pusillus is a Skenea ; I shall however soon have an op- 

 portunity of deciding, by seeing the animal. I am enabled to 

 state that the Modiola phaseolina is a mere variety of Modiola 

 modiolus, which when young, and indeed at all ages, varies both 

 in shape and lustre. — I have fresh proofs of the fixity of the 

 Foraminifera which shall appear shortly. — W. C. 



