JUKES-BROWNE : CEETACEOTTS AND EOCENE TENEEID^. 157 



Meek, in 1876,^ appears to have correctly appreciated its general 

 characters, for he adopted it as forming a subgenus in a large CalUsta 

 genus, and places it after Caryatis (= Pitaria). Dr. Dall, on the 

 other hand, separates it entirely from CalUsta, and puts it as a sub- 

 genus of the Venus puerpura group, which he chooses to call Cytherea 

 (Bolten, non Lam.) ; he gives no reason for this grouping, but in all 

 probability the point which weighed with him was the direction of the 

 anterior cardinal, for the hinge of the V. puerpura group is certainly 

 similar in that respect. 



Now it is interesting to find that shells of exactly the same general 

 facies as Conrad's Aphrodina tippana occur in European Eocene beds, 

 and that M. Cossmann had separated them from the other Cythereas of 

 the Parisian Eocene, when he revised the group in 1886 (op. cit.). 

 For these species he retained the name Cytherea (sensu stricto), and 

 the first on his list was C. nitidula, Lam., with which species the 

 C. lucida of Sowerby is identical. From examination of many speci- 

 mens of the latter I am able to recognize the left valves as answering 

 in every respect to the description of Aphrodina, and it follows that in 

 these Eocene shells we have the material for a complete description of 

 Conrad's genus or subgenus. I have therefore drawn up the subjoined 

 definition of it : — 



Shell oval, somewhat expanded anteriorly, surface smooth or finely 

 striate ; lunule slightly impressed, lanceolate and circumscribed ; 

 escutcheon not defined. Hinge with three divergent cardinals in each 

 valve ; in the left the posterior one is slightly bifid, the anterior is 

 thick, flattened in front, and curved forward; in the right the posterior 

 is broadly bifid, and the anterior small, slender, and directed forward. 

 The strong elongate anterior lateral of the left is received by a pit 

 between two small elongate teeth in the right valve. The nymphs are 

 corrugated in A. nitidula, but are said to be smooth in A. tippana. 

 The pallial sinus is large and deep, more or less ascending, and rounded 

 at the end. 



In general shape, in the character of the lunule, and in some 

 particulars of the hinge, Aphrodina shows a close resemblance to 

 CalUsta. It differs, however, in the dii'ection of the anterior cardinals, 

 in the feeble median, and in the grooved posterior cardinal of the left 

 valve. Moreover, I have not been able to detect any trace of radial 

 striation even in well-preserved Eocene specimens. 



"With regard to the rugosity of the anterior lateral, this is hardly 

 discernible in A. nitidula, so that I do not regard it as a group 

 character, but as a primitive character in the Cretaceous shell 

 {A. tippana). On the whole, therefore, I think Aphrodina should be 

 classed as a subgenus of CalUsta. 



Other Eocene species referable to Aphrodina are C. tranquilla, 

 Desh., and C. nitida, Desh. C. corbulina also probably belongs to 

 it, but C. despecta and C. Saincenyensis certainly cannot be included. 



1 Rep. U.S. Geol. Surv. Terr., vol. ix, p. 177. 



