JUKES-BROWNE : ON CALTASTA, AMIANTIS, AND PITAIilA. 343 



that, "on the whole, Tivelina is more nearly allied to Callista than 

 to any other genus." 



When drawing np the tabular view of genera and sub-genera for 

 my ])aper on Cretaceous and Tertiary Veneridae in 1908, I placed 

 Tivelina as an independent genus, but I now incline to regard it as 

 merely a sub-genus of Callida. Moreover, I think the species 

 Baudoni, elegans, and elegantula should be separated from it and 

 referred to Callista itself, from which they do not differ in any 

 essential respect ; and in this view I understand that M. Cossmann 

 concurs. On the other hand, I regard T. capsidoides as a ?,vaa\\ Pilar ia 

 belonging to the Calpitaria section; for there is nothing in the 

 dentition or the pallial sinus or the shape of the shell to dissociate 

 it from such species as P. sulcataria and P. Parisiensis. Meretrissa 

 {depressa and dubia) must also be separated and placed under the 

 genus Meretrix. 



While comparing the shells of Tivelina with the smallest species 

 of Callista, I came across the very small shells which have been 

 separated by Dr. Dall as a distinct genus under the name of 

 Transenella,^ and I noticed that the dentition of Tr. Conradina (his 

 type) is very like that of some species of Tivelina, i.e. those which 

 most resemble Callista. The chief differences are that in Transe^iella 

 the left posterior cardinal is rather longer and is partially free from 

 the nymph, and that the valve-margins are finely and tangentially 

 grooved, whereas in Tivelina they are smooth. It appears to be this 

 marginal grooving which has induced Dr. Dall to regard Transenella 

 as a genus, but I do not agree in considering this character to be of 

 generic importance. Such striation has probably less embryological 

 and structural value than crenulation of the margins, and yet both 

 smooth and crenulated mai'gins are found in the genera Circe and 

 Sunetta as well as in Astarte. Moreover, I have discovered that 

 similar tangential grooving occurs in Callista pannosa, Sow., and in 

 C. puella, Carp., shells from tlie Pacific coast of Central and South 

 America, which Dr. Dall has not hesitated to class as '■ 3facrocallista^ 

 ( Chionella), which is his equivalent for Callista. In the shells which 

 I believe to be puella the grooves are clearer than they are on the 

 thicker shells of C. pannosa, but probably they are equally distinct 

 on the young of the latter. I also find them to be well developed in 

 Callista angulifera. Sow., with specimens of which I have been 

 furnished h\ Mr. G. B. Sowerby, but unfortunately the locality of 

 this species is unknown. As all the other species which possess this 

 peculiar striation have their home in American waters, it is probable 

 that C. angulifera is also an American shell. Dr. Dall has described 

 four species from the Caribbean Sea, and one (the ' Psephis ' tantilla, 

 Gould) from the Pacific coast ; the three species above mentioned 

 raise the number to eight, and they certainly form a small group, 

 section, or sub-genus of Callista, which may well be recognized 

 under the name of Transenella. 



Another shell which certainly belongs to the Callista group and 



1 Proc. U.S. Nat. Mus., vol. vi, p. 340, 1883 ; vol. xxvi, p. 348, 1902. 



