172 TELLINID#. 
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. 
SusraMity DONACINA. 
Shell close, triangular, wedge-shaped, usually thick ; ligament 
short. 
Siphons short, separate, divergent. 
Donax, Linn., 1758. 
Etym.—Donaz, a sea-fish. (Pliny.) Wedge-shell. 
Syn.—Chione, Scop. Cuneus, Da Costa, 1778. Capisterium, 
Meuschen. 
Distr.—100 sp. United States, Norway, 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. (exii, 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. (exii, 82). 
HECUBA, Schum., 1817. Shell triangular, subcordiform ; ante- 
rior side sharply angulated, flattened, produced; two lateral 
teeth in each valve. D. scortum, Linn. (exii, 83, 85). 
SERRULA, Chemn. Shell oval-triangular, cuneiform, gibbous 
in front; margins denticulated within; hinge with oblong 
cartilage-fissure. D. trunculus, Linn. (ecxii, 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. 
HETERODONAX, Morch. Shell rounded-triangular, smooth, 
rather solid ; two lateral teeth in each valve. D. ovalinus, Desh. 
(exii, 87). 
EGERELLA, Stoliczka, 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 
