132 STUDIES IN GEOLOGY, No. 3 



soni, and the valves are more highly inflated anteriorly, 

 tapering off in greater contrast to a thin, produced posterior 

 ring which is much narrower and longer than that of nelsoni. 

 No specimens as large as those of nelsoni in the Nelson 

 collection have been found. C. berryi is very prolific in the 

 Lower Zorritos formation. Crassatellites reevei Gabb, 141 

 from Gatun, Santo Domingo, and Sapote, Costa Rica, is 

 somewhat similar, and is perhaps the closest species known 

 from the Americas. It differs chiefly in lacking the attenu- 

 ate posterior wing of berryi. In addition the area behind 

 the keel is flatter and smaller in berryi, the beaks being 

 higher and the keel more curved. 

 Lower Zorritos. Quebrada Zapotal. 



Superfamily LUCINACEA 



Family LUCINIDAE 



Genus PHACOIDES Blainville 



Subgenus PSEUDOMUVTHA Fischer 



Phacoides (Pseudomilthaf) insleyi n. sp. 



PLATE VII Fig. n. 



Shell medium-sized, moderately inflated, somewhat pro- 

 duced ventrally. Anterior dorsal margin broadly curved, 

 forming a blunt but perceptible angle with the lateral mar- 

 gin. Ventral margin full and rounded, somewhat produced. 

 Posterior dorsal margin similar to anterior, but the angle 

 with the lateral margin is more pronounced and is slightly 

 nearer the beaks. Umbones sharp, inclined forward, distinct. 

 General surface convex, excepting a slight concavity before 

 the beaks. There is no surficial sinus. Sculpture, of fine 

 concentric growth-lines, known only from small patches of 

 the epidermis, which is thin, and cleaves off readily, showing 



141 Brown and Pilsbry, Proc. Ac. Nat. Sci. Phila., vol. 64, p. 515, 

 pi. 24, fig. 5, 1912. 



