14 
PROCEEDINGS OF THE ACADEMY OF 
slightly concave upwards and inwards, sharply inflected inwards, forming a 
long, deep posterior escutcheon or cartilage base; ventral margin nearly 
straight, curving rapidly from a point opposite the beaks to the anterior ex¬ 
tremity, which is abruptly rounded into the deep heart-shaped lunette ; poste¬ 
rior extremity truncated by a line extending from the basal to the dorsal mar¬ 
gin, and making with the latter an angle of 120°. Yalves very ventricose, the 
greatest thickness being behind the central point on the sharp, prominent 
umbonal plication, which extends from the beak to the postero-basal angle— 
the area between this plication and the anterior region being curved subcylin- 
drically from a dorsal to a ventral direction, and the area between the plication 
and the hinge-line being a triangular, twisted, somewhat concave surface, 
faintly marked by lines diverging from the beak to the posterior boundary. 
Entire surface covered with fine irregular striae parallel with the basal and 
anal margins. 
Length -63 (100); height *29 (46); thickness of both valves *24 (38) ; height 
of posterior end *20 (32) ; length of anterior end *09 (14); of posterior end 
*54 (86). 
A peculiarity of this fossil is its cylindrical ventricosity and the posterior 
position of its greatest distension. (Compare Owen, Geol. Rep. Wis., Min., 
&c., Tab. III. a, fig. 18.) 
Sang-uinolites Iowensis, n. sp.—Shell of medium size, equivalve, transverse ; 
height equal to nearly one-half the length; beaks elevated above the dorsum ; 
subappressed, incurved and turned forward over a deep cordate lunette ; dor¬ 
sal line straight, reaching to near the posterior extremity of the shell; dorsal 
margin sharply inflected to form a long cartilage base ; ventral border gently 
curved, posteriorly receding toward the dorsum, and forming at the extremity 
an angle of 80° with the short, truncate, nearly rectilinear hind margin ; ante¬ 
rior extremity most projecting in the middle, from this point curving regularly 
to the ventral border and abruptly into the anterior lunette. Yalves ventri¬ 
cose, most inflated in the middle ; a sharp carina running sigmoidally from the 
beak to the postero-basal angle; another, still sharper, bounding the (poste¬ 
rior) escutcheon ; the twisted triangular space between these being marked, on 
the cast, by three faint depressed lines, radiating also from the beak. External 
surface marked by irregular lines of growth, strongest on the anterior portion 
and faintest on the dorso : umbonal surface. In some specimens apparently not 
separable from this species, a shallow groove runs from the ventral margin 
nearly opposite the beak, over the umbo. 
Length 1*03 (100); height *52 (50); thickness of both valves *38 (37); length 
of anterior end *21 (20) ; of posterior end *82 (80). 
The forms last mentioned above attain a size fully once and a half as large, 
The typical specimens of this species are quite distinct, but the larger ones 
approximate to S. amygdalinus in outline and characters of the dorsal region ; 
but they differ in being larger, more ventricose, and in having a sharp umbonal 
angle and acute posterior extremity. 
Sanguinolites sulciferus, n. sp.—Shell very small, transversely oblong, 
with nearly terminal beaks. Yentral margin broadly and rather deeply sinuate 
in the middle; anterior margin abruptly rounded below, terminating above in 
a deep lunette ; posterior margin somewhat produced below, suddenly rounded 
at the basal angle, and very obliquely truncate from thence to the end of the 
second third of the dorsal side, from which point the straight hinge-line ex¬ 
tends to the beak. Cardinal margins inflected to form a narrow, elongate 
escutcheon. Umbo full; umbonal ridge arcuate, with the convexity upwards, 
and terminating at the posterior basal angle ; space above this somewhat con¬ 
cave, longitudinally marked by seven or eight strong imbricating concentric 
ridges. 
Length *26 (100) ; height *14 (54); thickness of both valves *09 (35). 
'[Jan. 
