418 Ur. J. B.Gray o?i soine Families of Bivalve Shells. 



FOiit^^leJi^der; cylindrical, grooved in front. Shell internally 

 pearly; hinge toothless or nearly so. V'"'! ^ 



a. Pteriacna. Foot byssiferous. Mantle lobes fringed. Shell 

 eared, with a byssal notch in front. Cardinal teeth rudi- 

 mentary, horny, attached by byssus. 



)9. Crenatulina. Foot not byssiferous ; mantle fringed behind. 

 Shell not eared, without any anterior byssal groove ; hinge 

 toothless. Living in sponges. 



Suborder 3. Ostracea. Shell suborbicular ; anterior adductor 

 muscle obliterated, hinder large, central. Cartilage internal. 

 Mantle often bearded on the whole edge. 



A. Pectinina. Foot distinct, small, byssiferous or appendaged. 



Gills disunited medially. Tentacles separate from gills. 



4. Spondylidce, Syn. B. M. 1843, 83; P. Z. S. 1847, 201. Foot 

 short, thick, end with an enlarged truncate radiating disc, with 

 a central pedicelled ovate body ; lips foliaceous, pinnately lobed. 

 Mantle with bright ocelli. Hinge with two large interlocking 

 teeth. 



5. FectenidcE, Syn. B. M. 1842, 83 ; P. Z. S. 1847, 200. Foot 

 long, cylindrical, often byssiferous at the base. Mantle with 

 bright ocelli. Hinge of shell not, or only obscurely toothed. 



6. LimadcE. PectenidcT, Syn. B. M. 1842, 38; P. Z. S. 1847, 

 200. Foot compressed, not byssiferous. Mantle without any 

 ocelli on the edge. Shell gaping ; hinge toothless. 



B. Ostreina. Foot 7ione. Tentacles separate from the gills. 



7. Ostreida, Syn. B. M. 1842, 84; P. Z. S. 1847, 201. Shell 

 attached by the outer surface of one valve. Hinge toothless. 

 Tentacula short. 



8. Placentada, P. Z. S. 1847, 201. Placunida, Syn. B. M. 

 1842, 81. Shell free when adult. Hinge with two diverging 

 teeth. Animal ? 



C. Anomiaina. Foot small, cylindi'ical, truncate at the end, form- 



ing a laminal horny or strong byssus. Tentacles very long, 

 not distinct from the gills. 



9. Anomiada, Syn. B. M. 1842, 81 ; P. Z. S. 1847, 201. Foot 

 passing out through a slit in one of the valves and permanently 

 attaching the animal to marine bodies. Shell with two or three 

 subcentral scars. 



