76 PHOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



I have made inquiries, more particularly in regard to the A^itigona 

 and F(?H!!/'/co/r« group, with the following results : in Clausina verrucosa 

 the siphons are said to be completely separate, but there is no record 

 about those of Ventricola casina; I therefore applied to Professor 

 Herdman, who kindly informs me that in this species the siphons are 

 united for a great portion of their length, i.e. for about lialf their 

 extension outside the shell. Again, to Mr. H. Suter, of l^ew Zealand, 

 I owe the information that Ventricola ohlojiga has "short and rather 

 small siphons which are united to their tips ". There is, therefore, 

 great variation with regard to the union of the siphons in this genus. 



There seems to be an equal Lack of uniformity in the Venus and 

 Chione group, though they are usually united for about half their 

 external length. This is the case in Venm mercenaria as figured by 

 Dr. Dall himself;^ also in Chione gallina and Ch. fasciata, but in 

 Timoclea ovata they are united for three parts of their length, and 

 it is stated that the same is the case with some varieties of Ch. gallina. 

 In the case of Ch. grus, moreover, a West Indian species. Dr. Dall 

 himself states that " the animal has two subequal closely united 

 fringed siphons", so that his own statements are inconsistent with 

 one another. 



The facts above are sufficient to dispose of the theory, stated by 

 Dr. Dall as if it were a proved fact, that there is any correlation 

 between the anatomical characters of the aninuils and the presence or 

 absence of an anterior lateral tooth on the shell. On the other hand 

 I am decidedly of opinion that this anterior pustule or ' dentelon ' 

 has an intrinsic value of its own, for if it is the vestigial relic of an 

 anterior lateral tooth, then it represents an important structural 

 element in the dental armature of the hinge-plate. 



It may of course be argued that if Venus and Chione may be 

 descended from species of Antigona they should not be placed in 

 different sub-families, and to this there is no answer except that no 

 sub-families could then be recognized, and that it does seem useful 

 to emphasize the importance of looking for this little tooth, and of 

 using it as a basis of classification. 



Among the Venerince the groups which I recognize as having the 

 rank of genera are — Vetius, Protothaca, Sainarangia, Gomphina, 

 Gemma, dementia, Cgclina, Cyprimeria, Marcia, Tapes, Paratapes, 

 Baroda, and Venerupis. A few remarks on the taxonomic values of 

 certain groups may be useful to explain the connotation of these 

 genera and some of their divisions. 



In the first place I do not find any differences of real generic 

 importance between Venus (= Mercenaria) and Chione, so that I rank 

 the latter as a sub-genus of the former; nor is there any good reason 

 for the generic separation of Anomalocardia, which combines some 

 characters of Mercenaria with some of Chione. As a matter of fact 

 it would be more reasonable to separate those Chione which are 

 destitute of radial sculpture, such as rohoraia and tiara. It seems 

 more natural and convenient, however, to regard all these three 



1 Bull. U.S. Nat. Mus., No. 37, pi. Iv, 1889. 



