PANAMIC-PACIFIC PELECYPODA 299 



subobsolete sculpture, the concentric foldlike ribs developed only over a 

 small section of the beak and along the anterior submargins. The cord or 

 rib along the posterior-dorsal submargin is developed along the margins 

 of the beak only. 



This species replaces C. subrugosa south of Cabo Blanco, Peru, especi- 

 ally plentiful on the beach at Bayovar. It is a common fossil in the Peruvian 

 tablazos. 



Genus CHIONOPSIS Olsson, 1932 



{Gnidiella Parker, 1949, type species, Venus gnidia Broderip and 

 Sowerby). 



Type species by original designation, Chione amathusia Philippi. 



Shell of medium or large size, thin or of medium thickness, with large, 

 convex umbones ending in small adjacent beaks, generally placed at the 

 anterior one-third. Sculpture strong, consisting usually of thin, elevated, 

 distant, concentric lamellae between wider intervals, the edges of the larnel- 

 lae frilled or scalloped by smaller, radial riblets usually in pairs, the radials 

 showing best in the interspaces and on the ventral face of the concentric 

 lamellae. The escutcheon is narrow, lanceolate in shape, nearly the same 

 size in each valve, flat, smooth or sculptured with concentrics. The lunule 

 is small, cordate in shape, smooth or coarsely lamellose. The hinge has 

 three cardinal teeth in each valve, and of which, the left, middle cardinal 

 and the right, posterior cardinal teeth are bifid, the left, posterior cardinal 

 tooth is thin and long, the adjacent socket deep. Adductor scars are rela- 

 tively small. The pallial sinus is small but larger than in Chione, s.s. 



Ckionopsis is here considered a full genus, differing from Chione, s.s. 

 by its thinner, more convex valves, and by its larger and deeper pallial 

 sinus. The genus appears to have originated in the Pacific region and spread 

 into the Caribbean during the Miocene. It is represented in the Recent 

 fauna by several fine species. 



Chionopsis amathusia (Philippi) Plate 41. f'gure 7; 



Plate 51, figures 1, la; Plate 84, figure 2 



Venus amathusia Philippi, 1844, Abbild. und Besciireib. Conciiylipn, bd. 1, heft 5, Venus, 



p. 129 (7), pi. 2, fig. 4. Patria ? —Sowerby, 1853, Thes. Conch., vol. 2, p. 



709, pi. 154, figs. 26, 27. (These figures were referred to V. darivtnii Dunker 



by Romer and Lamy.) — Reeve, 1863, Conch. Icon., vol. 14, Venus, pi. 11, fig. 36. 

 Chione amathusia (Philippi), Olsson, 1924, Nautilus, vol. 37, p. 129. 

 Chione {Chione) amathusia (Philippi), Maxwell Smith, 1944, Panamic Marine Shells, 



p. 61, figs. 900, 901. 

 Chione {Chionopsis) amathusia (Philippi), Hertlein and Strong, 1948, Zoologica, vol. 



33, pt. 4, No. 13, pp. 183, 184.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. 



Hist., vol. 107, art. 2, p. 193. 

 Chione {Gnidiella) amathusia (Philippi), Parker, 1949, Jour. Paleont, vol. 23, No. 



6, p. 582, pi. 89, fig. 8; pi. 91, figs. 10, 12, 14. 



Shell ovate-triangular, convex, the umbones full and prominent, the 

 beaks small and curved slightly over a wide, cordate lunule, the posterior 

 side somewhat longer, its dorsal margin straight, descending into a nar- 

 rowly rounded end, the anterior margin deeply excavated in the lunular 

 region, rounded below it. Size is variable but seldom exceeding 58 mm. 



