PALEONTOLOGY ZORRITOS FORMATION 135 



spaces about equal in width ; in the right valve of worn 

 specimens the posterior five ribs are roughly bifid for their 

 entire length, and in the left valve a similar sulcation of the 

 posterior ribs is evident, but some of the bifurcations are 

 still more uneven, giving one of the paired ribs the appear- 

 ance of a secondary interstitial rib. These irregular ribs 

 represent the bases of spines which are lost on the specimens 

 available. Area, teeth, and inner shell unknown. Length, 

 31.25 ; height, 33.5 ; (semi) diameter, 15 mm. 



This species is superficially somewhat similar to C. peru- 

 vianum, but differs in being smaller and in having far fewer 

 ribs. C. phlyctaena Ball, 147 from the Ballast Point beds of 

 Florida, is similar, but differs in being less depressed an- 

 teriorly, and in having lower beaks. C. zorriiensis ap- 

 proaches C. taphrium Dall 148 from the Ballast Point and 

 Oak Grove beds of Florida, more closely than does C> peru- 

 vianum; however, taphrium is different in having narrower 

 interspaces between the ribs. " With the exception of its far 

 greater number of ribs, C. dominicense Gabb, 149 from Santo 

 Domingo, Costa Rica and Panama, is similar. It has the 

 bifid posterior ribs, and the general outline is similar, with 

 the exception that it is a much broader shell. 



Lower Zorritos. Quebrada Zapotal. 



Cardium (Trachycardium) peruvianuni n. sp. 



PLATE VIII Fig. i. 

 Cardium sp. ind., Nelson, Trans. Conn. Acad., vol. 2, p. 203, 1870. 



Shell large, inflated, evenly rounded. Marginal outline 

 unknown. Umbones prosogyrate, broad and full dorsally, 

 tapering rapidly terminally. Surface very convex, evenly 

 rounded, excepting the usual excavations before and behind 



47 Trans. Wag. Inst., vol. 3, pt. 5, p. 1097, pi. 48, fig. 13, 1900. 

 148 Idem., p. 1098, pi. 40, fig. 9. 



149 Toula, Jahrb. k.k. geol. Reichs., Bd. 58, p. 720, pi. 27, fig. 4, 

 pl. 28, fig. 1 8, 1908. 



