306 AXEL A. OLSSON 



Length 38 mm., height 31.2 mm., diameter 22 mm. Esmeraldas, 

 Ecuador. 



This is an abundant species throughout its range and in many places 

 is gathered as a food in enormous quantities. It is most plentiful in bouldery 

 or gravelly bars exposed at low tide. The shell is often marked with zig- 

 zagged transverse lines on a brown or white-brown base, occasionally uni- 

 color except for the beaks which may be white. These strongly patterned 

 shells have been given several names as indicated in the above synonym. 

 P. grata may be distinguished from the similarly marked shells of Nioche 

 asperrima histrionica by its average smaller size, typically more oblong 

 shape, much smaller lunule, and in the absence of a well-developed es- 

 cutcheon. 



Range— Gu\i of California to Peru, Chile. Costa Rica: Puntarenas. 

 Panama: Burica Peninsula; Puerto Armuelles; Ocones; Guanico; Bucaro; 

 Puerto Chame; Panama City; Chepillo; Pearl Islands. Colombia: Isla 

 Gorgona; Isla del Gallo. Ecuador: Limones; Camarones; Esmeraldas. Peru: 

 Lobitos, 



Genus NIOCHE Hertlein and Strong 



Type species by original designation, Venus asperrima Sowerby. 



Surface of shell with strong, radial costae, noded and rendered some- 

 what sharply scabrous by the intersecting concentrics, the costae often 

 becoming medially divided below or near the ventral margin. The lunule is 

 elliptical or cordate, not impressed and hence somewhat indistinct, usually 

 with finer sculpture, a darker color, and set apart by a fine, incised line. 

 A narrow, flat, smooth escutcheon is present in the left valve, absent or 

 nearly so in the right valve. The hinge armature has three cardinal teeth 

 in each valve; its most striking character is shown by the anterior cardinal 

 tooth of the left valve wh.ch is large, sharp, narrow, and lies parallel to 

 the lunular margin, and by its length and position resembles a lateral tooth, 

 its socket in the left valve is deep and curved. The central and posterior 

 cardinal teeth of the right valve and the central cardinal tooth of the left 

 narrow and produced to form the sharp, toothlike edge of the anterior 

 socket. The pallial sinus is short, the lunular and ventral margins finely 

 crenulated. 



Nioche was proposed by Hertlein and Strong as a subgenus of Chione, 

 its characters considered as intermediate between that genus and Proto- 

 thaca. In my opinion, its affinities seem much closer to Protothaca with 

 which it agrees in its surface characters and hinge. 



Nioche has recently been considered a synonym of Leukoma Romer, 

 1857 (type species by subsequent designation, Frizzell, 1936, Venus marica 

 Linne) by Myra Keen and classed as a subgenus of Protothaca. Judged 

 solely by the figures of Venus marica in Sowerby's Thesaurus, this treat- 

 ment does not seem correct. 



