344 PROCKEDINGS OF THK M ALACOLOGICAL SOCIETY. 



bears much external resemblance to Tivelina is the Venus Africana of 

 Philippi (= Chinne Jloridclla, Gray). This species was separated by , 

 Dr. Dall in 1902' under the name of Lepidocardia, and was placed i 

 for some inscrutable reason as a sub-j2;enus of his Cytherea (Bolten). , 

 I cannot see any kind of connexion between C. Africmia and Veiius > 

 puerpura or V. pllcata, with which it seems positively absurd to place ; 

 it. In its small size, faint striation, compressed form, and posterior r 

 attenuation it resembles Tivelina, but the hinge differs in the close ; 

 ap|)roximation of the anterior laterals to the cardinal teeth ; the 

 pallial sinus again agrees in form and direction with that of typical 1 

 Callista. The hinge-plate is very short and the cardinal teeth are ' 

 more equally divergent in both valves, the median occupying a more 

 central position than in Callista or Tivelina. It certainly has ■ 

 characters of its own which are not found in any other species, and 1 

 which entitle it to sectional or sub-generic rank in the genus Callista. 



Summary. 



The conclusions arrived at in the preceding pages may be summarized 

 in the form of a descriptive synopsis of the genera, thus : — 



Genus Callista (Poll), H. & A. Adams, 1857. 



Type. Venus chiotie, Linn. 



Synonyms: Chione, Gray (not Megerle, 1811) ; Diojie, Gray, 1847 

 (notHubner, 1816); Chionella, Cossmann, 1887. 



Shell oval, rarely trigonal, smooth or concentrically grooved, with 

 minute discontinuous ingrained radial striae beneath a glossy vernicose 

 periostracum. Lunule circumscribed, but escutcheon not defined. 

 Hinge of left valve with a strong anterior lateral and three cardinal 

 teeth, of which the two anterior are united to form a A, and the 

 posterior is confluent with the nymph ; in the right valve there are 

 two anterior laterals with a pit between them and three separate 

 cardinals, the median being nearer the anterior than the posterior, 

 and the latter is superficially grooved (only bitid in Aphrodina). 

 Pallial sinus generally wide, horizontal, and pointed in front. 

 Margins of valves smooth (except in Transenella). Anterior left and 

 posterior right dorsal margins grooved to receive bevelled edges of 

 opposite valve. 



Section Ilacrocallista, Meek, 1876. Type, Ve7ius nimhosa, Solander 

 {=V. gigantea, Gmel.). Shell much elongated, pallial sinus short. 



Section Callistina, J. -Br., 1908. Type, Cytherea plana. Sow., 

 Cretaceous fossil. Left posterior cardinal long and not confluent 

 with the nymph. Left anterior lateral elongate, narrow, corrugated; 

 right laterals obsolete. Pallial sinus ascending. 



Sub-genera. 



Aphrodina, Conrad, 1868. Type, Meretrix tippann, Conrad. 

 Shell like Callista, but finely striated, and without trace of radial 

 striation. Left posterior cardinal partially free, and anterior cardinal 



' Proc. U.S. Nat. Mus., vol. xxvi, p. 356. 



