14 PROCEEDINGS OF THE ACADEMY OP 



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. Valves 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-liue 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 striaj 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.) 



Sanguinolites 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 biod margin ; ante- 

 rior extremity most projecting in the middle, from this point curving regularly 

 to the ventral border and abruptly into the anterior lunette. Valves 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 103 (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 sdlciferds, n. sp. Shell very small, transversely obloDg, 

 ' with nearly terminal beaks. Ventral margin broadlj and rather deeply sinuate 

 in the middle; anterior margin abruptlv 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. 



