138 Studies in Geology, No. 3 



not noded, but both forms show the prominent yet fine con- 

 centric lines in the interspaces. The ribs of aMnis are a 

 trifle broader mesially. C. castum Guppy/^^ from Manzan- 

 illa, Trinidad, is somewhat similar, but is more rounded in 

 shape, and not as high ; in addition it has nodulose ribs which 

 are not as broad as those of afiinis, and are of greater num- 

 ber. Both forms show the cross-lining of the interspaces. 

 Another Trinidadian species, C. carolinae Maury,^^* from 

 beds of Chipolan age, is similar in general outline, but has 

 the rib-nodulation common in Trigoniocardia, and absent 

 in afiinis. Other features are entirely similar. C. reniformis 

 Koenen,^^^ from the lower Oligocene of north Germany, is 

 similar, being very close in shape, but it has more ribs, the 

 upper surfaces of which slope anteriorly — those of aMnis are 

 flat-topped — but the fine cross-striation of the rib-surfaces is 

 similar. 



Lower Zorritos (base). Quebrada north of Boca Pan. 



Superfamily VenERACEa 



Family VENERIDAE 



Subfamily Dosiniinae '^ 



Genus Dosinia Scopoli 



Section Dosinidia Dall 



Dosinia (Dosinidia) grandis Nelson 



Plate VIII— Fig. 4. 



Dosinia grandis Nelson, Trans. Conn. Acad., vol. 2, p. 201, 1870. 



"Shell large, solid, subequilateral ; length and breadth 

 nearly equal, broadest just above middle line. Beaks ele- 



'■"'^ Quart. Jour. Geol. Soc. Lond., vol. 22, p. 582, pi. 26, fig. 4, 

 1866. 



'"'Jour. Ac. Nat. Sci. Phila., 2nd. ser., vol. 15, p. 54, pl- 9, figs. 

 5, 6, 1912. 



^''Abh. geol. Spez. Preuss. Bd. 10, Hft. 5, p. iiS4, P- 77, figs. 

 9, 10, II, 1893. 



