138 CORBULIDA. 
Shell equivalve, globular or suboval, very inequilateral, widely 
gaping posteriorly ; a spoon-shaped process and small cardinal 
tooth in each valve; ligament double, external and internal ; 
pallial impression very short and simply arcuated. 
Siphon very short, truncated, scarcely extending beyond the 
valves. Lives in indurated clay at the mouths of rivers, in 
Senegal. 
Famity CORBULID A. 
Shell small, inequivalve, thick, gaping in front; binge con- 
sisting of 2 single recurved tooth in one valve, received into a 
fosset or notch in the other. 
Animal unsymmetrical; mantle closed except in front, the 
narrow opening dentate; siphons united, short, fringed. Living 
in the sand or mud on the seashore or in estuaries. 
CorsbuLa, Bruguiere. 
Etym.— Corbula, a little basket. 
Syn.—Hrodina, Daud. (== Pacyodon, Beck.) Agina, Turt. 
Distr.—i3 sp. United States, Norway, Britain, Mediterranean, 
West Africa, China. Inhabits sandy bottoms; lower laminarian 
zone—80 fathoms. Fossil, 120 sp. Inferior Oolite—; Europe, 
India. Laramie—; United States. CC. Mediterranea, Costa (ev, 
93). C. sulcata, Brug. (cv, 94). 
Shell thick, inequivalve, gibbose, closed, produced posteriorly ; 
right valve with a prominent tooth in front of the cartilage-pit; 
left valve smaller, with a projecting cartilage-process; pallial 
sinus sight; pedal scars distinct from the adductor impressions. 
Animal with very short, united siphons; orifices fringed; anal 
valve tubular; foot thick and pointed; palpi moderate; gills 
two on each side, obscurely striated. 
THNIODON, Dunker, 1851. Shell ovately elongated; subequi- 
lateral, smooth, equivalve, and apparently closed, right valve 
with a cardinal tooth under the umbo extending forwards, left 
valve with a distinct marginal cartilage-pit behind the beak. 
Type, 7. ellipticus, from liassic beds near Halberstadt (Germany °. 
The ligament was partially external, partly internal, the valves 
not gaping. 
ANISORHYNcCHUS, Conrad. Shell nearly or quite equivalve, 
transversely pyriform, the posterior side being rostrate ; beaks 
nearly equal, and distinctly incurved. Hinge, muscular and 
pallial impressions as in Corbula, except that the cardinal tooth 
is furrowed. 
C. pyriformis, Meek. Associated with fresh- and brackish- 
water types. 
PACHYODON, Gabb, 1868. (Anisothyris, Conr.) PP. obliqua, 
Gabb (cvii, 83-35). Associated with marine and estuary types. 
