OF SOUTHERN INDIA. 251 



(h). To these three divisions I add provisionally a fourth one, which Gabb (Pal. 

 Calif., ii, 1869, p. 188,) proposed for his /' Loripes dubms and named CUssocolns. 

 The shell is sub-orbicular, thin, with the ligament lodged in a deep groove, the 

 right valve has the hinge margin slightly thickened under the beak, the left with 

 an obsolete tubercle ; " pallial line unknown," but I hardly expect that the shell 

 is different from the second group of Loripes I mentioned. 



c. Sere, Gabb, 1866, (Pal. Calif., ii, p. 28). Shell sub-orbicular, globose, con- 

 centrically striated, anterior lateral and cardinal teeth well developed, as in Lucina, 

 but the lunule is very deep, extending across the hinge area between the anterior 

 lateral and the cardinal teeth. Type, Luc. [Here] Hichihofeni, Gabb, from tertiai'y 

 beds of California. It seems very doubtful that the excavation of the lunule is 

 a character sufficient for separating this shell from Lucina, unless there is some 

 difference in the internal structure and the muscular impressions, as is, for instance, 

 the case in P/ji/is. Gabb suggests that two recent species living on the Pacific 

 coast should also be referred to Here, Luc. excavata. Carp., and another, with 

 six large rounded ribs, occurring in the Gulf of California. If we, however, 

 principally base the sub-genera upon the character of ornamentation, the costate 

 species would rather be referable to the next group. 



d. Codakia, Scop., 1777. Shell sub-orbicular or obliquely oval, compressed, 

 radiately ribbed, the areal edges behind the beaks almost entirely enclosing the 

 ligament, hinge-teeth regular and generally complete; type, Luc. tigerina, Linn. 



e. IHltha, H. and A. Adams, 1857. Shell roundly ovate, rather high, 

 concentrically striated, and more or less distinctly radiately ribbed ; hinge with the 

 lateral teeth sometimes obsolete ; type, Luc. Childreni, Gray. As this species shows 

 fine radiating ribs, the more distinctly ribbed but sub-orbicular species, like 

 Luc. scabra, Lam., and others, could be referred to this sub-genus, if not to Codakia, 

 for many of that group, referred by H. and A. Adams to Myrtea, possess well 

 developed lateral teeth. 



/. Myrtea, Turt., 1822. Shell ovately elongated with a long hinge area, 

 compressed, concentrically striated, hinge with the lateral teeth sometimes obsolete ; 

 type, Luc. spinifera, Mont., sp. The only other recent species which should be re- 

 tained in this sub-genus is Luc. fabula, Heeve; all the others noted by H. and A. 

 Adams may better be placed in 3Iiltha. Forms of the typical species, Ltic. spinifera, 

 already occur in Jurassic and cretaceous rocks, and some of those have the 

 lateral teeth distinct, others not, but the shape of the shells appears to remain 

 constant. 



g. Lirodiscus, Con., 1869, (Ain. Journ. Conch., v, p. 46). Shell sub-quadran- 

 gular, concentrically ribbed, posterior side lobed by an impressed line ; hinge with 

 two cardinal teeth in each valve, right valve with a small pyramidal anterior lateral 

 tooth, left with a posterior one distant from the cardinals ; type, Ast. tellinoides. 

 Con., from eocene rocks. The author suggests that the cretaceous Astarte sinuata, 

 d'Orbigny, may belong to the same genus. I believe it to be a sub-genus of 

 Lucina, and it seems doubtful whether it be sufficiently distinguishable from Myrtea. 



3 Q 



