156 PROCEEDINGS OF THE MALACOLOGICAL SOCIETr. 



This subgenus is certainly intermediate between CalUsta and Pitaria, 

 and its existence makes it difficult to regard these two larger groups as 

 separate genera. How many Eocene species will have to be referred 

 to Calpitaria I cannot yet say, but think the following belong to it : 

 C. amhigua, Desh., C. Saincenyensis, Desh., C. Suessoniensis, Desh. 

 ( = fenuistriafa, Sow.), C. fastidiosa, Desh., and C. elegans. Lam. 



Callistina, n.sect. 



One of the earliest representatives of the CalUsta group is the well- 

 known ' Cytherea plana,^ Sow., from the so-called 'Greensand' of 

 Blackdown. This has the cardinal teeth of CalUsta, but the left anterior 

 lateral is a long narrow ridge, grooved or corrugated on the sides, and 

 fitting into a shallow corrugated pit in the right valve, which pit 

 occupies only a small area in the flat anterior part of the hinge-plate. 

 This part of the plate, in fact, resembles Dosinia more than CalUsta. 

 The surface of the shell is smooth, and as a rule, nothing but con- 

 centric lines of growth are visible, but a specimen in the Sedgwick 

 Museum shows some irregular radial striae like those of CalUsta. 

 The pallial sinus is ascending and subangularin C. plana, but in some 

 other species it is rounded. C. sulplana, d'Orb., and C. polymorpha, 

 Zittel, belong to the same group, for which I propose the name 

 CalUstina, with C. plana, Sow., as the type. 



4. Aphkodina, Conrad (genus or subgenus). PI. VI, Fig. 4. 



This name was given to an American Cretaceous shell which Conrad 

 had previously described as Meretrix tippana. Though he had only 

 a single left valve before him at the time, Conrad made this the type 

 of a new genus, ^ which he described as follows : — " Generic character. — 

 Shell rounded or suboval, striated or sulcated ; hinge in the left valve 

 with three diverging cardinal teeth, the anterior tooth as thick as the 

 middle or thicker, and a straight compressed transversely rugose 

 lateral tooth parallel with the margin of the shell above it ; pallial 

 sinus deep and similar to that in Caryatis, Eoemer." 



The figure given by Conrad shows that the anterior cardinal curves 

 forward so as to point directly to the anterior lateral ; also that the 

 pallial sinus is wide, deep, and subangular. The type has quite recently 

 been figured and described by Mr. Stuart Weller,'^ but he calls the 

 shell Meretrix tippana, without saying anything of Conrad's proposed 

 genus, and his description of it is short. Moreover, he states that the 

 right valve has only two cardinal teeth, which must be either a mis- 

 print or a mistake, for Dr. Dall describes it as having three cardinals 

 in each valve, as indeed the structure of the left valve would lead us 

 to expect (Synopsis cit., p. 355). 



The generic affinities of this shell do not seem to be properly under- 

 stood even in America, and in Europe it has practically been ignored. 



1 Amer. Journ. Conch., vol. iv (1869), p. 246, pi. xviii, fig. 5. 



2 " Eeport on the Cret. Palseont. of New Jersey" : Geol. Survey of N.J., 



vol. iv of Pal. Series, pi. Ixviii, figs. 1 and 2 (1907). 



