PANAMIC-PACIFIC PELECYPODA 187 



measurements. Length 30 mm., height 24.7 mm., diameter of closed valves 

 20 mm. Distinction between the Panama shell and typical C. spurca from 

 Peru (Callao) appear slight, the more southern form is generally more 

 rounded in shape and the ribs heavier. 



Range — Panama to Mexico. Panama: Panama Bay (Mr. S. Jadis). 

 Costa Rica: Punta Arenas (Hertlein), Mexico: Off Manzanillo, Colima. 

 (Hertlein). 



Subgenus STROPHOCARDIA, new subgenus 



Type species, Cardita megastropha (Gray). 



Shell rounded cordate, solid, with high umbones and strongly proso- 

 gyrately coiled beaks over a small, deeply sunken lunule. Dorsal-posterior 

 margin flattened, escutcheon-like. Sculpture formed by relatively few, low, 

 rounded ribs. Hinge plate massive, the right valve with a large, stout, more 

 or less hooked cardinal tooth, the left valve with two cardinal teeth and 

 a large central socket; no vestigial laterals. 



This group is represented in the Recent fauna by C. megastropha 

 (Gray) and by several fossil species in the Tertiary. The group differs so 

 strikingly in shape and hinge characteristics from C. cuvieri (Broderip) 

 and its allies that it deserves separate recognition. 



CardJta (Strophocardia) megastropha (Gray) Plate 26, figures 5, 5a 



Venericardia megastropha Gray 1825, Ann. Phil., new ser., vol. 25, p. 137, two figs. 



p. 138.— Lamy, 1922, Jour, de Conchyl., vol. 66, No. 4, p. 294, two text figs., 



p. 296. 

 Venericardia flammea Michelin, 1831, Mag. de Zool., vol. 1, Moll., pi. 6. 

 Cardita tumida Broderip, 1832, Proc. Zool. Soc. London, p. 56. — Reeve, 1843, Conch. 



Icon., vol. 1, Cardita, pi. 5, fig. 26. 

 Cardita varia Broderip, 1832, Proc. Zool. Soc. London, p. 56. — Reeve, 1843, Conch. 



Icon., vol, 1, Cardita, pi. 5, fig. 25a. 

 Cardita megastropha (Gray), Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 3, No. 



8, p. 106. (Type locality selected La Plata Island, Ecuador). 



Shell of medium or large size, solid, cordate, the ventral side rounded, 

 the dorsal trigonal, with high umbones and strongly coiled beaks. The 

 anterior-dorsal side is deeply impressed with a small, flattened lunule lying 

 under and partially overhung by the beaks. Sculpture and appearance of 

 specimens vary according to their freshness and degree of wear; perfectly 

 fresh specimens have a dark-brown, coarsely, concentrically striated perio- 

 stracum through which the ribs show rather obscurely; in beach specimens 

 or those cleaned by acid or alkaline, the ribs assume greater prominence 

 and are seen to be low, trigonal in section, their interspaces also trigonal 

 and with a central line, their color is a reddish-brown often variegated by 

 •white and brown blotches. Interior white with the margins of the valves 

 weakly furrowed by the ends of the ribs. 



Length 57.8 mm.; height 58 mm.; diameter 44 mm. Manglaralto, 

 Ecuador. 



Range — Gulf of California southward to Ecuador and the Galapagos 

 Islands. Panama: Pearl Islands: Bucaro. Colombia: Gorgona Island. 

 Ecuador: Esmeraldas; Sua; Isla la Plata; San Pedro near Manglaralto. 



Subgenus PLEUROMERIS Conrad, 1867 

 Type species by monotypy, Pleuromeris decemcostata Conrad ( = 



