GEOLOGICAL SURVEY OF THE TERRITORIES. 315 



rounded ; pallia! margin semiovate in outline ; posterior margin nar- 

 rower than the other, and subtruncate ; dorsal outline sloping gradually, 

 with slight convexity behind the beaks, and more abruptly in front ; 

 beaks rather depressed, oblique, and placed about one-third the length 

 of the valves from the anterior extremity ; surface only showing very 

 obscure lines and somewhat stronger ridges of growth. 



Length, 2.24 inches ; height at the beaks, 1.48 inches ; convexity, ap- 

 parently about 0.40 inch. 



The specimens of this species are all more or less flattened by acci- 

 dental compression, but show the outline and surface characters per- 

 fectly, even to remains of the thin epidermis. With considerable diffi- 

 culty I have succeeded in clearing away the matrix so far as to see that 

 the hinge margin is comparatively strong for so thin a shell. It shows 

 apparently three diverging cardinal teeth in each valve, and a linear 

 anterior lateral tooth extending parallel to the anterior margin, while 

 the posterior lateral teeth are somewhat remote from the cardinal, and 

 rather elongated. On these posterior lateral teeth I have seen fine trans- 

 verse striee, which doubtless also exist on the anterior lateral, though I 

 have not seen a specimen in a condition to show them. 



Internal casts show the anterior muscular impression to be ovate, and 

 the posterior broader, or more nearly circular, while the pallial line 

 shows a shallow, rounded sinus, forming less than a semicircle. 



Locality and position : Hallville coal mines, just above a bed of coal, 

 in a black, argillaceous, rather hard rock, that may be shaly at some 

 places. 



COKBICULA? CEASSATELLIFORMIS, (MEEK.) 



Shell attaining about a medium size, longitudinally ovate-subtrigonal- 

 compressed, very thin and fragile; anterior side rounded ; pallial mar, 

 gin forming a semiovate curve, being more prominent anteriorly than be- 

 hind ; posterior side longer than the other, but much narrower, being 

 very narrowly truncated at the immediate extremity ; dorsal margin 

 forming a long straight slope behind the beaks, and sloping more abrupt- 

 ly in front; beaks rather depressed, oblique, and located rather more 

 than one-third the length of the valves from the anterior margin ; 

 posterior umbonal slopes showing some tendency to form a very slight 

 prominence from the beaks toward, the posterior basal extremity. Sur- 

 face marked with fine lines, and a few irregular, stronger ridges and 

 furrows of growth. Hinge not well made out. 



Length, 0.95 inch ; height, 0.60 inch ; convexity, about 0.20 inch. 



This form will be distinguished from the last, not only by its much 

 smaller size, but by its more trigonal outline (caused mainly by the 

 greater obliquity and straightness of its posterior dorsal slope), the 

 greater j>rominence of its post-umbonal slopes, and its proportionally 

 stronger ridges of growth. I have not seen its pallial line and know lit- 

 tle of its hinge, though some of the specimens seem to show indications 

 of three diverging cardinal teeth, as in the last. Like that species, it 

 is a very thin, fragile shell. 



In form and general appearance, this shell is much like Cyrena {Cor- 

 uicula) angustata, Deshayes (An. Saus. Yert. Bassin de Paris, 1, p. 508, 

 PI. XXXVII, Figs. 9, 10, 11 et 12), but it not only attains a larger size, 

 but differs in being more attenuated posteriorly, and more distinctly 

 truncated at the immediate extremity of the narrowed posterior end. 



Both this and the last-described species very nearly resemble some of 

 the depressed, elongated species of Grassatella, in outline, and belong 



