234 University of California Publications in Geology IT' 



more nearly obsolete, and by the long, straight, anterior dorsal margin. 

 The hinge also differs in having the weak, narrow resilifer and long, 

 narrow laterals, this being especially true of the anterior teeth. 



Occurrence. — At locality 2991, upper Etchegoin, on Zapato Creek, 

 Fresno County ; at the type locality this species occurs with Thracia 

 formosa, n. sp., Fissuridea unica, n. sp., Tegula (Chlorostoma) pulcella, 

 n. sp., and the associated fauna. 



THKACIA FORMOSA, n. sp. 

 Plate 9, figures 4, 4a 

 Type specimen no. 11103, Univ. Calif. Coll. Invert. Palae. 



Shell small, inequilateral, thin, moderately compressed. Beaks 

 low, about three-fifths length of shell from anterior end. Posterior 

 dorsal margin slightly convex ; posterior end truncated. Junction of 

 anterior dorsal and ventral margins marked by slight increase in con- 

 vexity. Ventral margin evenly arcuate. Surface ornamented by dis- 

 tinct, uniform, rounded, concentric ridges ; with a well developed, 

 broad sulcation extending from the beak to the posterior extremity. 

 Hinge weak ; right valve with small, rather thick tooth projecting at 

 angle of nearly 45 degrees to plane of shell. Dimensions : height, 

 27 mm. ; width, 19 mm. 



Occurrence. — At locality 2991, with a large fauna characteristic 

 of the upper Etchegoin. 



FISSURIDEA UNICA, n. sp. 

 Plate 11, figures 3, 3a, 3b 

 Type specimen no. 11100, Univ. Calif. Coll. Invert. Palae. 



Shell subovate, conical, elevated, straight to slightly convex sides, 

 with apex a little anterior. Ornamented by numerous prominent, 

 rounded, rather thin, radiating ridges with narrow interspaces. In- 

 cremental lines unequal, often more prominent than the radiating 

 ridges. Apical orifice oblong, anterior to the apex, bounded inside by 

 a posteriorly truncated callus. Dimensions of type, which is a rather 

 small specimen : height, 14 mm. ; maximum diameter, 25 mm. ; mini- 

 mum diameter, 19 mm. 



This species can readily be recognized by its height, ovate base, 

 and radial ribbing with narrow interspaces. 



Occurrence. — In the upper Etchegoin, with a large fauna of the 

 Pecten coalingensis zone at locality 2991. 



