PANAMIC-PACIFIC PELECYPODA 307 



Nioche (Nioche) asperrima asperrima (Sowerby) Plate 53. figures 3. 3a: 



Plate !)4, figure 6 



Venus asperrima Sowerby, 1835, Proc. Zool. Soc. London, p. 42 Lobos Islands. — 



Sowerby, 1853, Thes. Conch., vol. 2, p. 714, pi. 155, figs. 57, 58.— Reeve, 1863, 



Conch. Icon., vol. 14, Venus, pi. 6, figs. 19a, 19b. 

 Chione (Nioche) asperrima (Sowerby), Hertlein and Strong, 1948, Zoologica, vol. 33, 



pt. 4, No. 13, p. 187. 

 Protothaca {Leukoma) asperrima (Sowerby), Keen, 1958, Sea Shells of Tropical West 



America, p. 149, fig. 341. 



Shell subcircular to subovate, generally coarse, moderately convex, 

 sculptured by rather coarse, rasplike, radial costae, the surface in the type 

 form, dull, chalky white, somet.mes irregularly blotched with brown. The 

 stronger radials are usually simple and uniform in size on the umbones 

 but below, on the middle of the disk, they are generally dissected so that 

 they become double, paired and sometimes triparted near the ventral 

 margin. The costal intervals are deep, narrow grooves. Both the costals 

 and their intervals are crossed by strong, corded concentrics producing a 

 pattern like that of a coarse lattice. 



An average specimen measures: Length 50.7 mm., height 45.7 mm., 

 diameter 29 mm. 



Nioche (Nioche) asperrima histrionxa (Sowerby) Plate 53, figures 4, 4a, 6 



Venus histrionica Sowerby, 1835, Proc. Zool. Soc. London, p. 41 Real Llejos and Santa 

 Elena.— Sowerby, 1853, Thes. Conch., vol. 2, p. 714, pi. 155, fig. 52.— Reeve, 

 1863, Conch. Icon., vol. 14, Venus, pi. 16, fig. 70. 



Tapes tumida Sowerby, 1853, Thes. Conch., vol. 2, p. 697, No. 64, pi. 146, figure 42 

 Columbia. 



Shell usually smaller, ovate to oblong, plump and solid, the average 

 length seldom over 45 mm. The sculpture is produced by small, cordlike 

 costae crossed by evenly spaced, raised, corded concentrics producing a 

 finely reticulated pattern; the costals on the middle and anterior surface 

 of the disk are usually double or paired; simple on the posterior portion; 

 between the primary concentrics there are usually five or six threads of 

 growth. The lunule is cordate, generally large, not impressed, radially 

 sculptured, brown in color, and circumscribed by a small line. There is a 

 small, narrow, flat escutcheon in each valve; the escutcheon of the right 

 valve overlaps the margin of the left valve slightly. The ground co^r is 

 usually white, with three or more, discontinuous, radial rows of brown or 

 finger-like markings, the posterior slope is usually more deeply colored. 

 Interior white or purple. '1 he pallial sinus is distinct and reaches about a 

 quarter of the distance in. 



Length 45.7 mm., height 37.3 mm., diameter 25.2 mm. Puerto Chame, 

 Chorrera, Panama. 



Typical Nioche asperrima is a Peruvian shell, first described from 

 specimens obtained on the Lobos Islands. It is common along the shores 

 of Sechura Bay, rare further north where it is replaced by the smaller and 

 more colorful subspecies A^. histrionica. Occasional forms of the two sub- 

 species are so close that they can hardly be separated; hence they are 

 treated here together. The typical subspecies is a large, coarse shell, sub- 

 circular in form, with a plain, dull surface of a white or chalky gray color, 

 its radial riblets coarse and harsh to the touch. More common to the north, 



