146 PROCEEDINGS OP THE ACADEMY OP 



little more removed from the buccal margin ; surface (of specimens with the 

 epidermis wanting) showing obscure lines of growth, crossed by very fine in- 

 distinct irregular radiating striee ; ligament long ; hinge much thickened at the 

 anterior end of the valves, composed of two rough irregular cardinal teeth in 

 the left valve, and one more prominent tooth in the right ; lateral teeth long 

 and slightly arched ; dorsal cicatrix located nearly under the beaks, not very 

 deep ; anterior cicatrix distinct, and strongly corrugated ; cavity of the beaks 

 shallow. Length about 2-60 inches; height 1-33 inches; breadth about 1-18 

 inches. 



Named in honor of Rev. Chester Dewey, of Rochester University. 



Locality and position. Bed G. of the freshwater and estuary formations at 

 the mouth of Judith River. (See section at that place.) 



Unio subspatdlata. 



Shell moderately thick, oblique, elongate-ovate, rather compressed, most con- 

 vex at the anterior end, cuneate behind ; buccal end wider than the other, 

 abruptly rounded or subtruncate; posterior end narrowly rounded ; base nearly 

 straight or very slightly concave ; dorsal margin sloping a little, with a long, 

 convex curve from near the umbone?, towards the posterior end; beaks small, 

 not much elevated, located at the anterior end ; surface (epidermis gone) show- 

 ing faint lines of growth, crossed by fine irregular, radiating striae; hinge and 

 interior unknown. Length 2-83 inches ; height 1-34 inches ; breadth -75 inch. 



This species is related to U. Danai of this paper, but is more compressed, and 

 its base and flanks are less contracted. It likewise presents the well marked 

 difi'erence of having terminal beaks, while those of U. Danai are removed 

 about one-fourth the length of the shell back from the anterior end. 



From TJ. Dcwcijanus of this paper, to which it is also related, it differs in 

 being more elongated and compressed. It is also more arched on the back and 

 more contracted along the lower border. 



Locality and position. Same as last. 



Pectunculus subimbrioatus. 



Shell transversely oval, nearly circular, not much compressed, equilateral ; 

 extremities rounded, posterior end sometimes slightly broader than the other : 

 base rather more broadly rounded ; cardinal border slightly arched, moderately 

 thick ; beaks (obtuse?) not much elevated or incurved ; surface ornamented by 

 about fifty simple, rounded, depressed radiating plications, a little more than 

 twice a« broad as the grooves between, crossed by numerous regular, distinct, 

 imbricating lines of growth, which arch upwards in crossing the costse ; 

 cardinal teeth about twenty-five, not large, lateral ones arcuate, with the con- 

 cave sides turned from the beaks ; ligament area moderate, marked by about 

 six grooves, which form very obtuse angles under the beaks ; muscular im- 

 pressions large but not deep. Length 1-49 inches ; height 1-36 inches ; breadth 

 1-02 inches. 



Associated with the above we have a single valve of another individual not 

 more than one-sixth as large, and having comparatively a smaller ligament 

 area, fewer teeth and rather less prominent beaks. The costse are also ap- 

 parently obsolete over proportionably larger spaces at the extremities of the 

 hinge. This we suspect may be a distinct species, but without more specimens 

 for comparison we are unwilling to so regard it at present. If it should prove 

 to be a different species we would suggest for it the name of P. suborbiculatus. 



Locality and position. Heart River, near junction of No. 5 with the Tertiary, 

 but perhaps in the former. 



OSTREA GLABllA. 



Shell elongate-ovate, rather irregular, usually curving to the left, but some- 

 times to the right; generally narrower near the beaks than at the other ex- 



[May, 



