1'7Q' TEIiLTNltiiE. 



Shell compressed, thin, suborbicular, two divergent, lamellar 

 teeth in the right valve, three in the left valve, the middle one 

 bifid ; muscular impressions oval, polished ; pallial line with a 

 profound, ascending sinus. 



Mantle-margins plain, pedal opening contracted ; foot basal, 

 pointed. 



Subfamily DONACIN^. 



Shell close, triangular, wedge-shaped, usually thick ; ligament 

 short. 



Siphons short, separate, divergent. 



DoNAX, Linn., 1Y58. 



Etyra.—Donax ^ a sea-fish. (Pliny.) Wedge-shell. 



Syn. — Chione, Scop. Cuneus, Da Costa, 1778. Capisterium, 

 Meuschen. 



Distr. — 100 sp. United States, Norwaj'^, Baltic, Black Sea, 

 all tropical seas. In sands near low-water mark ( — 8 fathoms), 

 buried an inch or two beneath the surface. Fossil, 45 sp. Cret. — ; 

 United States, Europe. D. denticulatus, Linn, (cxii, 80, 81). 



Shell trigonal, wedge-like, closed; front produced, rounded ; 

 posterior side short, straight ; margins usually crenulated ; 

 hinge-teeth 2*2 ; laterals 1 — 1 in each valve ; ligament external, 

 prominent; pallial sinus deep, horizontal. 



Animal with the mantle fringed ; siphons short and thick, 

 diverging, anal orifice denticulated, branchial with pinnate cirri ; 

 foot very large, pointed, sharp-edged, projected quite in front ; 

 gills ample, recumbent, outer shortest ; palpi small, pointed. 



LATONA, Schum., 1817. Shell oval, cuneiform, compressed 

 behind, truncated in front ; margin simple within. D. cuneatus, 

 Linn, (cxii, 82). 



HECUBA, Schum., 1817. Shell triangular, subcordiforra ; ante- 

 rior side sharply angulated, flattened, produced ; two lateral 

 teeth in each valve. I), scortum, Linn, (cxii, 83, 85). 



SERRULA, Chemn. Shell oval-triangular, cuneiform, gibbous 

 in front ; margins denticulated within ; hinge with oblong 

 cartilage-fissure. Z>. trunculus, Linn, (cxii, 86). 



CAPSELLA, Gray. Shell oval-oblong, transversely elongated, 

 subrounded at the extremities ; covered with a greenish epider- 

 mis ; margins of valves smooth within. D. acutangulus, Desh. 



HBTERODONAX, Morch. Shell rounded-triangular, smooth, 

 rather solid ; two lateral teeth in each valve. D. ovalinus, Desh. 

 (cxii, 87). 



EGERELLA, StoKczka, 1870. (Egeria, Lea, 1833, not Roissy or 

 Leach.) Shell elongated, subtrigonal, anterior side much shorter 

 than posterior; hinge with two cardinal teeth in each valve, one 

 of which is bifid, lateral teeth none, sometimes they are indicated 



