310 AXEL A. OLSSON 



marked with concentrics only and bordered on the disk side by a small, 

 scabrous cord, usually white in color: the right valve has no escutcheon, 

 the dorsal margin at this point is much enlarged, inrolled so as to resemble 

 a large fold. The lunule is small, elliptical in shape, and brown in color. 

 Surface of the disk is finely sculptured with small, flattened riblets, simple 

 on the umbones, more or less divided ventrally. Color is mostly a dull 

 white except for the lunule and the escutcheon which is brown. The pos- 

 terior section of the ventral margin is crenulated. 



Carpenter's types of th's species have not been figured but there are 

 manuscript drawings made by Carpenter in the library of Mollusca of the 

 United States National Museum. A^. squamosa is closely allied and possibly 

 equivalent to N. grus (Holmes) of the southeastern United States which 

 occurs both in the late Tertiary and Recent faunas. N. squamosa has been 

 recorded as a Pleistocene fossil in California under the name of N. picta. 



Range — Lower California to northern Peru. Panama: Puerto Armuelles. 

 Ecuador: Puerto Callo; Santa Elena. Peru: Zorritos; Bayovar. 



Subgenus ANTINIOCHE, new subgenus 



Type species Nioche {Antinioche) beili, new species. 



Shell subcircular and strongly convex, regularly cancellated by uni- 

 formly spaced, narrow concentric lamellae, finely crenulated on their ven- 

 tral side and with stronger, rounded, radial riblets in their interspaces. 

 Lunule cordate, not depressed, defined by an incised line and sculptured 

 predominantly by radial ribs, wrinkled by the lines of growth. The es- 

 cutcheon is a flattened, smooth band confined to the left valve. Hinge 

 that of Nioche, the left anterior cardinal tooth being high, narrow, and 

 elongated nearly parallel to the lunular margin; the anterior limb of the 

 base of the right middle cardinal tooth is narrowly elongated so as to 

 form the lower rim of the anterior cardinal socket. The adductor scars 

 are relatively large, subequal and rounded, the pallial sinus short and 

 narrow. 



Antinioche resembles Periglypta by its cancellate sculpture but has the 

 hinge pattern of Nioche. 



Nioche (Anlinloche) beili, new species Plate 50, figures 1, la, 4 



The shell is of medium size, subovate, rotund, with the beaks placed 

 near the anterior one-fourth, convex, solid, the posterior-dorsal side nearly 

 straight but distally passing smoothly into the circular curve of the posterior 

 and ventral margins. The lunule is large, covering much of the anterior- 

 dorsal side, elliptical, its margin somewhat flaring and circumscribed by 

 an incised line, sculptured by strong ribs, waved or undulated by lamellae 

 of growth; the escutcheon as described for the subgenus. The general sur- 

 face of the convex disk is cancellated by the intersection of radial and 

 concentric sculptural elements; the concentrics are widely and evenly 

 spaced, raised lamellae spaced about 2 mm. apart, the radials are simple, 

 cordlike costals between the concentric lamellae. The concentric lamellae 

 are curiously ornamented on their ventral surface by short, double ribs 

 which stand vertical like short columns in the small, narrow grooves be- 

 tween the radials. On the anterior and posterior slopes, the concentric 

 lamellae are high and waved. General color of the surface is a creamy 



