Zoological Society. 219 



covered with radiating veins, while the lower is generally punctated, 

 appears to be the one which gives rise to the muscle that is attached 

 to the inner surface of the plug. 



* Shell plicately folded. Perforation of lower valve small, firmly 

 embracing the plug. Placunanomia. 



1. Placunanomia Cumingii. 



Shell depressed ; edge of the valves with three or four large angular 

 folds. 



Placunanomia Cumingii, Broderip, Proc. Zool. Soc. 1832, 29; 

 Sow. Genera, t. ; Manual, t. . f . 



Hab. Central America ; Gulf of Dulce, Province of Costa Rico. 



** Shell ovate, radiately ribbed ; edge not plicated. Perforation of 

 lower valve moderate, firmly embracing and inclosing the plug. 



PODODESMUS. 



t American. 



2. Placunanomia rudis. 

 White ; disk brown ; smooth laminae. 



Upper valve with two roimded separate scars of nearly equal size, 

 the hinder one rather more transverse. 



Placunanomia rudis, Broderip, Proc. Zool. Soc. 1834, 2. 



Pododesmus decipiens, Philippi, Wiegmann Arch. i. 1837, 387. 

 t. 9. f. I (one scar left out). 



Hab. East Indies ? Broderip. Havana ; Philippi. West Indies ; 

 Brit. Mus. 



3. Placunanomia foliata. 



White, smooth laminae, veith very sUght, distant, radiated ribs ; 

 disk purple brown. 



Upper valve with two nearly united scars ; the upper largest, and 

 rather elongated ; lower small, rounded, 



Placunanomia foliata, Broderip, Proc. Zool. Soc. 1834, 2. 



P. echinata, Broderip, Proc. Zool. Soc. 1834, 2. 



" P. pectinata, Brod." in Mus. Cuming. 



Hab. Eastern Columbia, Bay of Guayaquil. Isle of Muerte ; Bro- 

 derip. Martinique, n. 6, and Brazils, n. 7 ; Mus. Cuming. Jamaica 

 (upper valve of young only) ; Rev. L. Guilding ; Brit. Mus. 



The specimen of Placunanomia echinata, from the island of Nevis, 

 in Mr. Cuming's collection, appears to be only an imperfect specimen 

 of this species. Mr. Broderip doubted if this might not be the case, 

 when he described it. 



4. Placunanomia abnormalis. 



White, radiated, ribbed. 



Upper valve with two scars, confluent on the lower hinder edge ; 

 the upper one rather the largest. 



" Placunomia abnormalis. Sow." in Brit. Mus. 



Hab. West Indies. 



These three species are very nearly related to each other, and if it 

 were not for-the difference in the position of the scars, might be taken 



15* 



