434 AXEL A. OLSSON 



shaped. The chondrophore is a grooved, narrow plate in the left valve, and 

 projects more than in the other Caryocorbulinae. 



This group of Corbulas is distinguished from other members of the 

 family by its unusually thin and delicate shell; by its high angled posterior 

 keel and its elegant sculpture. Fossil species are known from the Miocene 

 of Peru. 



Tennicorbula tennis (Sowerby) Plate 77, figures 3, 3a 



Corbula tenuis Sowerby, 1833, Proc. Zool. Soc. London, p. 36. "Hab. in America Centrali". 



—Reeve, 1843, Conch. Icon., vol. 2, Corbula, pi. 2, fig. 13.— C. B. Adams, 1852, 



Ann. Lyceum Nat. Hist., New York, p. 523. — Maxwell Smith, 1944, Panamic 



Marine Shells, p. 68, fig. 869B. 

 Corbula glypta Li, 1930, Bull. Geol. Survey of China, vol. 9, p. 264, pi. 5, figs. 38, 38a. 



(See Pilsbry, 1931, Proc. Acad. Nat. Sci. Philadelphia, vol. 83, p. 431). 



The shell is thin, white, elongate, subrectangular in shape, and strongly 

 inequilateral, the umbones high and full and placed nearly in the middle. 

 The posterior side is strongly contracted and bears a sharp, elevated, um- 

 bonal keel. The rostral area is flattened or deeply impressed; in the middle 

 of which there is an elongated escutcheon also defined by an angled keel. 

 Surface ornamented with coarse, concentric riblets over the whole disk 

 and also on the rostral area. There is usually a mild sulcation across the 

 disk from the beak to the middle of the ventral margin. 



Length 21.2 mm., height 13.2 mm., diameter 15.4 mm. Palo Seco, 

 Panama Canal Zone, 



A rare but widely distributed species. 



Range — Panama to northern Peru. Panama: Montijo Bay (Cuming); 

 San Carlos; Biicaro. Panama Canal Zone: Palo Seco; Venado Beach. 

 Colombia: Isla del Gallo. Ecuador: Puerto Callo; Santa Elena. Peru: Zor- 

 ritos. 



Genus PANAmCORBULA Pilsbry, 1932 

 Type species by original designation, Corbula (Panamicorbula) inflata 

 (C. B. Adams) {Potamomya inflata C. B. Adams). Panama. 



Shell moderately large, of medium weight, subovate, convex, sub- 

 equivalve, the beaks submedian, the anterior side a little longer, rounded, 

 the posterior side shorter, its dorsal margin sloping to a bluntly truncated 

 end. Posterior-dorsal area wide but defined externally by a weak angle. 

 Surface smoothish or sculptured only by irregular growth incrementals. 

 Hinge: the right valve has the usual large or small, hook-shaped cardinal 

 tooth in front of the deep pit, but on the margins on each side, equidistant 

 from the beak, there are deep, lateral sockets, their inner edge thickened 

 to resemble a lateral tooth; the left valve has no lateral teeth, the margins 

 merely beveled so as to fit into the sockets of the opposite valve. Chondro- 

 phoral plate in the left valve is similar to that of Caryocorbula but wider. 

 Adductor scars large, subequal, the pallial sinus absent or weak. Color 

 white, the periostracum thin, yellow or light brown. Habitat: "In soft im- 

 palpable mud, under a mangrove thicket, near high water margin, and near 

 the outlet of a small stream, with Area tuberculosa" C. B. Adams. Two 

 species seem recognizable. 



