188 AXEL A. OLSSON 



Cardita tridentata decemcostata Conrad). Miocene to Recent of the eastern 

 Atlantic seaboard of the United States. 



Shell small, stout, convex, broadly triangular and equivalve. Umbones 

 submedian, prominent, ending in small, adjacent beaks. Sculpture formed by- 

 large, coarsely noded, radial ribs. Hinge of Cardita but with small lateral 

 teeth consisting of a posterior socket and an anterior tooth in the left valve 

 and their counterparts in the right. Lunule small, restricted to the left 

 valve, the escutcheon minute and poorly defined. 



Cardita (Pleuromeris) guauica, new species Plate 25, figure 8 



Shell small, white, obliquely ovate, the height and length are nearly 

 equal, the anterior side a trifle longer, oblique, the umbone convex, ending 

 in a small, slightly prosogyrate beak. The shell is moderately solid. There 

 is a slightly flattened area along the posterior-dorsal margin and a small, 

 flattened lunular surface in the right valve. Sculpture formed by about 17 

 low, axial ribs set-off by incised grooves, all finely granulated or noded. 

 Hinge shows a large central cardinal tooth bordered by a small socket on 

 each side and a faint anterior lateral socket in the right valve. 



Length 3.2 mm., height 3.3 mm., diameter 1.1 mm. (right valve). Holo- 

 type, ANSP 218925. 



The description of this species is based on a single right valve from 

 Guanico, probably not fully mature but it is recorded here as representing 

 the only Pleuromeris known from this part of the coast. In shape, it some- 

 what resembles P. armilla Dall from the Gulf of Mexico, but its anterior side 

 is much longer and its size smaller. 



Range — Panama. Panama: Guanico. 



Genus CARDITAMERA Conrad, 1838 

 (Lazaria Gray, 1854, type species L. radiata Sowerby.) 



Type species by monotypy, Cypricardia arata Conrad. Miocene and 

 Pliocene of the eastern and southeastern United States. 



Shell elongate, oblong, equivalve, the margins closed. Umbones and 

 beaks placed much nearer the anterior end, the posterior side drawnout, 

 often wider and more strongly sculptured. Hinge pattern that of Cardita 

 but with lateral teeth and sockets weakly or strongly developed in both 

 valves; the middle, right cardinal tooth smaller, its base drawnout into a 

 long, slender, lamina-like arm extended posteriorly along the lower edge 

 of the hinge plate. Sculpture formed by radial ribs, usually strong on the 

 posterior side, often flattening and fading out anteriorly. 



Two species occur in the Panama-Ecuadorian region belonging to 

 two subgenera. 



Key to subgenera of Carditamera 



I. Lunule in both valves. Posterior-umbonal slope low. Lateral teeth 

 quite strong. 



Subgenus Carditamera, s.s. 

 IL Lunule small or absent. Posterior-umbonal slope elevated and angular. 

 Lateral teeth small to vestigial. 



Subgenus Byssomeria, new subgenus 



