418 Dr. J. E. Gray on some Familks of Bivalve Shells. 



Foot slender, cylindrical, grooved in front. Shell internally 

 pearly ; hinge toothless or nearly so. 



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

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

 mentary, horny, attached by byssus. 



^. 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. 1842, 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. Pectenida, Syn. B. M. 1842, 83; P. Z. S. 1847,200. Foot 

 long, cylindrical, often byssiferous at the base. Mantle wi]^ 

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



6. Limadce. Pectenidse, Syn. B. M. 184.2, 38; P. Z. S. 1847, 

 200. Foot compressed, not byssiferous. Mantle without any 

 ocelli on the edge. Shell gaping ; hinge toothless, fi^ia^nuii 



B. Ostreina. Foot none. Tentacles separate from the gills. 



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

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

 Tentacula short. •> j'jo/i 



8. Placentada, P. Z. S. 1847, 201. Placunidse, Syn.M:M' 

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

 teeth. Animal ? 



C. Anomiaina. Foot small, cylindrical, 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. 



