136 Studies ix Geology, No. 3 



the beaks. Sculpture of about 50 sharply defined, square, 

 strong- ribs, with channelled interspaces equally broad ; 

 spines may have existed, but the specimens available are 

 worn. Area and hinge normal. Inner margins unknown. 

 Length, 46; height, 46; (semi) diameter, 18.5 mm. 



This species is very similar in appearance to C. domin- 

 iccnse Gabb,^'"'" from Santo Domingo, Costa Rica, and Pan- 

 ama, differing in being more nearly round in outline, thus 

 of broader proportions, with five to ten less ribs which are 

 distinctly separated by channelled interspaces ; in domin- 

 icense the interspaces are rather merely the sides of the 

 closely adjacent ribs. In dominicense the tops of the ribs 

 slant anteriorly; in pcniznanum they are parallel to the sur- 

 face of the shell. C. taphrium Dall,^^^ from the Ballast Point 

 and Oak Grove beds of Florida, is similar in shape, but has 

 only 34 instead of 50 ribs. 



Zorritos formation. Zorritos. 



Subgenus FRi\GUM Bolten 



Section Trigoniocardia Dall 



Cardium (Trigoniocardia) affinis (Nelson) 



Plate VIII — Figs. 2, 3. 



Hcinicardia affiiiis Nelson, Trans. Conn. Acad., vol. 2, p 204, 1870. 



Shell small, high, inflated, obovate, heart-shaped viewed 

 from behind. Anterior margin rounded, joining through a 

 blunt angle w^ith the descending, almost straight ventral 

 margin. Posterior marginal angle prominent and acute; the 

 posterior margin ascends from the lowest point of the shell 

 almost vertically in a straight line, curving more or less 

 abruptly into the posterior dorsal margin. Beaks high, erect. 



'■'■"Trans. Amer. Philos. Soc, vol. 15, n.s., pp. 250-251, 1873; 

 also Toula. Jahrl). k.k. geol . Reichs.. vol. 58, p. 720, pi. 27, fig. 4, 

 pi. 28, fig. 18, 1908. 



'■'•'Trans. Wag. Inst., vol. 3, pt. 5, p. 1098, pi. 40. ^S- 9, 1900. 



