308 AXEL A. OLSSON 



especially along the coasts of Ecuador and Panama, is the smaller and 

 longer shell, more highly colored, and to which Sowerby gave the name 

 histrionica. The extremes of histrionica and asperrima are so different that 

 they deserve recognition, although at times, the classification of some in- 

 tergradational specimens is entirely arbitrary. Nioche asperrima histrionica 

 is often found with Protothaca {Tropithaca) grata (Say) which it much 

 resembles. 



Range — Gulf of California southward to Peru. Nioche asperrima 

 asperrima Panama: Panama City; Old Panama; Puerto Chame, near 

 Chorrera; Guanico. Peru: Bayovar; Lobos Islands. Nioche asperrima his- 

 trionica Costa Rica: Puntarenas. Panama: Puerto Armuelles; Rey Island, 

 Pearl Islands. Colombia: Isla del Gallo. Ecuador: Pedernales; Puno Island. 



Nioche (Nioche) metodon (Pilsbry and Lowe) Plate 55, figures 3, 3a 



Chione metodon Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Pliiladelphia, vol. 84, 



pp. 100, 101, pi. 15, figs. 7-11 Montijo Bay, Panama. 

 Chione {Nioche) metodon Pilsbry and Lowe, Hertlein and Strong, 1948, Zoologica, vol. 



33, pt. 4, p. 187. 



The shell is generally small (length 27 to 100 mm.), triangular-rotund, 

 convex or plump, solid, light-buff in color with some dull violaceous angular 

 markings and small spots, the lunule and escutcheon dark brown in solid 

 color or in brown bars alternate with white on the escutcheon. The lunule 

 is large, nearly flat, circumscribed by a small line, the escutcheon principally 

 defined in the left valve, flattened, smooth, much smaller or absent in the 

 right valve. On the umbones, the sculpture is formed by small, rounded 

 riblets crossed by low concentric threads, larger and slightly lamellose at 

 the ends. Below the middle of the disk, the riblets are a trifle wider and 

 flatter, and towards the ends, they have a tendency to divide into three, 

 small cords of about the same size as the individual crenulations along 

 the ventral margin. On the anterior slope, the sculpture is a little coarser 

 than elsewhere. The lunule is radially sculptured and because of its brown 

 color stands out prominently. PaUial sinus small. 



Length 40.7 mm., height 38 mm., diameter 32 mm. Montijo Bay, Pan- 

 ama. Type, ANSP 155571. 



Length 26.4 mm., height 24 mm., diameter 18.5 mm. Bahia Honda, El 

 Lagartillo, Panama. 



Range — Panama. Panama Canal Zone; Venado Beach. Panama: 

 Montijo Bay (Pilsbry and Lowe); El Lagartillo, near Las Tablas. 



Nioche (Nioche) zorritensis, new species Plate 53, figures 5, 5a; 



Plate 55, figure 6 



The shell is small or of medium size, triangular, rotund, convex, the 

 posterior side a trifle longer, the two ends of nearly equal roundness. The 

 lunule is elliptical, flat, sculptured with coarse, scabrous riblets, brown 

 in color and bordered by an incised line. The escutcheon is developed best 

 only in the left valve; it is narrow, flat, smooth or with concentric lines 

 only. On the umbonal surface, the sculpture is finely cancellate, produced 

 by small, simple, rounded riblets between narrow, flat intervals and more 

 distantly spaced, low, concentric lamellae; below the middle of the disk, 

 the riblets are wider and carry on the top of each, three to five threads 

 which at the lower end match in size the individual crenulations along 



