130 AMERICAN MARINE CONCHOLOGY. 
2. S. NAVALIS, Linnzeus. Figs. 275-280. 
Syst. Nat., edit. x. 651. 1758. 
Valves about equal in length and breadth, the posterior auricle 
expanded somewhat laterally, its base extending lower than that 
of the anterior area; anterior area moderate, the basal-margin 
convex, inclining somewhat obliquely downwards to the fang, its 
junction considerably higher up than that of the posterior auricle ; 
posterior auricle not ascending, but produced laterally, its dorsal 
edge mostly somewhat concave, lateral margin nearly straight, a 
little oblique, rounded at each end; fang acuminating rapidly 
towards the base ; internally, the apophysis is broad but thin, not 
thickened at the end, and of the same breadth throughout, and 
the position of the posterior auricle is defined by a close, project- 
ing rim; pallets convex on one side and plane on the other, the 
stalk, which is about as long as the blade, moderately thick and 
flexous, not continued as a rib beyond the commencement of the 
blade ; tube not concamerated. 
Valves and pallets each 6 mill. in length. 
New England and Middle States. , (Eur.) 
3. T. MEGoTARA, Hanley. Figs. 281-283. 
Brite Concheie ieuteeletwostm lO, uentyes. 
Breadth and altitude of valves subequal; the posterior auricle 
large, broadly rounded on the margin, raised above the beak and 
terminating below much further down than the anterior auricle ; 
the auricle is not defined within by a projecting shelf; pallets 
spoon-shaped, with truncate apex, with slender, cylindrical stalks, 
on the concave side forming a rib to the apex of the blade. 
New England, (Hur.) 
4. T. Norvaaica, Spengler. Figs. 287-291. 
Skrivt., Nat. ii., 102, t. 2, f. 4-6, 1792. 
Valves solid, higher than wide, the beak elevated beyond the 
dorsal margins of the auricles; auricles small, terminating at less 
than one-half the length of the shell. Pallets spade-shaped, trun- 
cate at the tip with a stem about as long as the blade; scarcely 
defined on the centre of the latter. Tube solid, concamerated. 
Height 18, breadth 13 mill. 
New England (rare, Hur.). 
This is the largest and most solid species occurring on our 
coast; its great proportionate length, elevated beaks, and the 
