TnTRAri,ODON 1 199 



in the left, obliquely or feebly vertically striate ; beak cavities 

 deep, rounded ; anterior scars impressed ; nacre bluish-white. 



Length yj, height 55. diam. 41 mm. 



Length 68, height 50, diam. 40 mm. 



Tropical South America east of the Andes. 

 Castalia quadrilatera d'ORiviCNY, Guer. Alag., 1835, p. 42; \'oy. 



Am. Men, 1843, P- 599' pl- Lxxiii. 

 Tetraplodon quodrilatentm Simpson, Syn., 1900, p. 864. 

 Mya ambigua Wood, Ind. Test. Rev., 1856, p. 200, pi. i 



(supp.), fig. 9. 

 Castalia acitticosta Hupe. Moll. Nouv., IH, 1857. p. yy, pi. xiv. 



fig. 3. — SowERBY, Conch. Icon., XVII, 1869, pi. iii, figs. 12, 



12a, 12b. 

 Castalia latiquadrata Sowerp.y, Conch. Icon., XVII, 1869, pi. 



Ti, fig. 10. 



Close to ambiguns, but larger, thinner, less inflated, with 

 stronger, wider ribs, which are more developed on the posterior 

 slope than in that species. The hinge is more delicate, the later- 

 als less vertically striate 



Tetraplodon cordatus (H. and A. Adams). 



Shell but slightly inflated, triangular rhomboid, inequilateral ; 

 beaks full, high, widely rounded, having numerous, rounded, 

 radial ridges separated by grooves about their own breadth, 

 the central ridges coalesce below and all end on a line about 

 midway over the disk; posterior ridge high, slightly double 

 below, sharp above, ending in a blunt point at the base of the 

 shell ; dorsal line straight, short, meeting- the oblique posterior 

 truncation at a decided angle ; base line nearly straight ; surface 

 with decided, concentric sculpture; epidermis olive; nacre 

 bluish. 



Length 87, height 65 mm. 



British Guiana. 

 Castalia cordata H. and A. Adams, Gen. Rec. Moll, II, 1857, 



p. 509, III, pi. cxx, figs. 2, 20. — SowERBy, Conch. Icon., 



XVII, 1869. pi. II, fig. 8. 

 Tetraplodon qiiadrilatcnim. (part), Simpson. Syn., 1900, p. 



864. 



