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1445 



TERTIARY FAUNA OF FLORIDA ^ "^ 



minute, the valves brightly colored, living in pure salt water. West Africa 

 and the tropics of the New World. 



PSection Egetaria Morch. T3'pe C. piillastra Morch. 



Shell tapetiform, radiately, minutely striated ; the anterior laterals adja- 

 cent, the posterior laterals distant ; the pallial sinus very deep, ascending. 

 Pacific coast of Costa Rica. 



I have not seen this species, which is unfigured. 



Section Isodoma (Deshayes) Cossmann. Type /. cyprinoides Deshayes. 

 Parisian Eocene. 

 Valves Cythereiform, thin, with delicate hinge and entire pallial line, the 

 anterior end shorter, the laterals short, prominent, and smooth. 



The dentition of this section was misunderstood by Deshayes, whose work 

 has been corrected by Cossmann. It seems to bear to the oriental Cyrena such 

 a relation as Psendocyrena does to Polymesoda. I have not seen specimens. 



Subgenus Leptesthes Meek. T3'pe Corbicula fracta Meek. Eocene of the 

 Wahsatch. 



Shell large, solid, subrostrate, compressed, elongate-ovate ; cardinals as in 

 Cyrena, strong; anterior laterals subadjacent; posterior laterals distant, short, 

 separated from the cardinals by a broad, flat hinge-plate ; pallial line with a 

 short, wide, triangular sinus ; the lunule defined by an incised line ; ligament 

 elongated. 



This appears nearer to Cyrena than to Corbicula; the short, low lateral 

 laminae are not crenate, and I do not find them even distinctly striated. 



Diodus Gabb does not appear to differ essentially from Polymesoda. 



According to White, in his discussion of our non-marine fossil Mollusca, 

 two typical species of Cyrena appear in the Cretaceous of Dakota, C. dakotensis 

 and C. Carletoni Meek, but there is nowhere any figure or description of the 

 hinge or pallial line, and their allocation must remain doubtful until this is 

 supplied. 



Only one species of what appears to be a true Cyrena is known from our 

 Tertiary, and as this is represented by silicious pseudomorphs which do not 

 show the pallial line, even this may belong to the section Polymesoda. 



Csrrena poinphol3rx Dall. 

 Plate 38, Figures 7, 8. 

 Cyrena pompholyx Dall, Trans. Wagner Inst., iii., pt v., p. 1194, pi. xxxviii., figs. 7-8, 

 1900. 



