TLACUNANOMIA. 565 



Genus PLACUNANOMIA, Broderip. 



Shell ovate. Byssal notch distinct, converted into a hole 

 by the upper part of the anterior lobe of the notch being 

 soldered to, and forming part of, the cardinal edge. Plug 

 triangular, gradually enlarging in size; apex and outer 

 surface next to the body to which it is attached calcareous, 

 longitudinally striated ; inner surface covered with horny, 

 longitudinal, parallel lamina?, and more or less agglutinated 

 to the edge of the notch. Upper or dorsal valve with 

 two sub-central muscular scars, the upper scar radiately 

 veined. 



Ex. P. macrochisma, Deshayes, pi. 129, fig. 2. P. 

 Cumingii, Broderij), fig. 2, a. 



The type of this genus, P. Cumingii, was dredged by 

 Mr. Ouming in the Gulf of Dulce in Central America ; 

 the other species are from the West Indies, California, 

 Australia, and Europe. They live attached to dead shells, 

 stones, and coral. 



Sub-gen. pododesmus, Philippi. 



Shell with the surface of the valves radiately ribbed. Perfo- 

 ration of lower valve moderate, firmly embracing and enclosing 

 the plug. 



abnormalis, Sow. rudis, Brod. 



foliata, Brod. 



VOL. II. 4 D 



