188 TRIGONIA. 



costata ; area postica lata, obtuse angulata ; marg-ine ventrali 

 convexo. — Obliquely ovate, rather flat, nearly equal in height 

 and depth ; posterior area obtusely angular. The name was 

 afterwards changed by Lamarck to T. pectinata. The 

 following is probably different. 



4. DUBiA, f. 5, Soiverhy. — Subrhomboidea, subventricosa, 

 extus fusco purpurea, distanter nodoso-costata ; area postica 

 subquadratim truncata margine dorsali subdeclivi ; margine 

 ventrali rectiusculo. — This and the preceding seem to differ 

 in shape and proportions. The present being the more 

 rhomboidal and the dorsal area more broadly truncated. It is 

 now the commoner species and distinguished as such in the 

 trade. It is a more gibbous shell than the true T. marga- 

 ritacea. 



5. Stranqei, f, 8, A. Adams. — Subrotundata ventricosa ; 

 area postica abbreviato subangulata ; costis magnis confertis, 

 nodis verrnciformibus approximatis ornatis ; margine ventrali 

 convexissimo. — A rounded species, remarkable for the close, 

 regular, wart-like tubercles on the ribs. 



