PANAMIC-PACIFIC PELECYPODA 227 



Genus ECHDfOCHAMA Fischer, 1887 



Type species by monotypy, Chama arcinella Linne, 1767 {Arcinella 

 Schumacher, 1817, not of Oken, 1815). Recent, Florida, and the West 

 Indies. 



Shell equivalve, solid, usually attached in the early stages only, be- 

 comes free in the adult. Sculpture is formed by rows of radial ribs, sometimes 

 developing strong spines and separated by interspaces which may be deeply 

 pitted, reticulated, or netted. Umbones prominent, developing into strongly 

 spirally coiled prosogyrate beaks. A large, deeply impressed lunule defined 

 by an incised line is present. Hinge and ligament as in other members of 

 the family. 



Echinochama arcinella californica Dall Plate 34, figure 3 



Echinochama californica Dall, 1903, Proc. U. S. Nat. Museum, vol. 26, No. 1342, p. 



950, pi. 62, fig. 5. — Maxwell Smith, 1944, Panamic Marine Siiells, p. 56, fig. 



716. — Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 3, No. 8, p. HI. 

 Echinochama arcinella californica Dall, Nicol, 1952, Jour. Paleont. vol. 26, No. 5, p. 



806, pi. 119, fig. 8. 



This is the Pacific subspecies of the Caribbean E. arcinella arcinella 

 (Linne) from which it differs mainly in that the outline of the adult shell 

 is angular or subtriangular, particularly in the right valve, while the an- 

 terior lobe is more sharply separated from the rest of the shell. It is a rela- 

 tively rare shell. A larger subspecies occurs fossil on the Burica Peninsula 

 in beds assigned to the Pleistocene. 



Range — Gulf of California southward to Coiba Island, Panama. 



Superfamily CTRENOIDACEA 

 Family CTKENOEDIDAE 



A group of small, brackish-water clams, generally orbicular in shape 

 with the small beaks nearer the anterior end, thin, the surface covered by 

 a brown or olive-colored periostracum. The hinge is typical, provided with 

 a thin, 7-shaped cardinal tooth in each valve and a smaller, lamellar, V- 

 shaped cardinal below it in the right valve; there are no laterals. Ligament 

 external. Pallial line generally indistinct, entire. 



Genus CYEENOBDA Joannis, in Guerin, 1835 

 {Cyrenella Deshayes, 1836; Cyrenodonta H, and A. Adams, 1857.) 



Type species by monotypy, C. dupontia Joannis. Senegal. 



Shell subovate, rounded, convex, usually thin, with the beaks and um- 

 bones placed anterior of the middle line, prosogyrate. Hinge with two cardin- 

 al teeth, the right anterior one double, no laterals. Ligament external. A 

 large, weakly defined lunular area is sometimes present. Adductor scars 

 normal, connected by a simple pallial line. Sculpture formed by fine, hair- 

 like, often wrinkled, concentric lines and covered by a brown or olivaceous 

 periostracum. Brackish. 



The type species, C. dupontia from Africa is large, attaining a length 

 of 35 mm. or more but most South American species of the genus are small 

 or medium-sized shells and are easily mistaken for Diplodonta if collected 



