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 affinis are a 

 trifle broader mesially. C. castum Guppy, 153 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 affinis, and are of greater num- 

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

 Another Trinidadian species, C. carolinae Maury, 154 from 

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

 the rib-nodulation common in Trigoniocardia, and absent 

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

 Koenen, 155 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 affinis 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. 



154 Jour. Ac. Nat. Sci. Phila., 2nd. ser., vol. 15, p. 54, pi. 9, figs. 

 5, 6, 1912. 



LW Abh. geol. Spez. Preuss. Bd. 10, Hft. 5, p. 1154, p. 77, fi g s - 

 9, 10, ii, 1893. 



