222 yciv Species of Fussils fro/zi Ohio. 



Allorisma Aiidrc^i'si, u. sp. 



Pal. O. Vol. Ill, Plate 10, Fig. «. 



Shell of medium size or smaller, transversely elliptical in outline ; the 

 length being about twice the height, and the thickness a little more than 

 two-thirds the height. Valves ventricose, most rotvmd a little in advance ot 

 the middle and along the umbonal ridge, and wedge-shaped posteriorly, as 

 seen in a cardinal view ; beaks of moderate size, slightly projecting al)ove 

 the hiuge-liue, incurved, directed anteriorly, and situated at about one-sixth 

 of the entire length from the anterior end. Cardinal line straight or ap- 

 pearing slightly concave, extending about three-fourths of the length of the 

 shell from the beaks backward, and bordered by a proportionally large and 

 wide escutcheon. Anterior end short, sloping forward from between the 

 beaks, at about an angle of forty-five degrees to the hinge-line, to near the 

 middle of the height of the shell, and then abruptly rounding backward into 

 the somewhat regularly convex basal margin. Posterior end broadly rounded 

 from the point of the umbonal ridge to the extremity of the cardmal line. 

 Anterior end of the shell characterized by a very small lunule. Surface of 

 the shell marked by several strong concentric undulations or folds, which 

 are simple, and regularly increase in size and strength to near the full size 

 of the shell ; but near the outer margin of the valves, in the specimen figured, 

 they are smaller and doubled by the interpolation of an intermediate rib. 

 The undulations are crossed obliquely from the beak to the basal margin, 

 just posterior to the middle, by a narrow, almost imperceptible sulcus, and 

 along the crest of the umbonal ridge by a line of low-convex and faintly- 

 marked nodes, one on the surface of each undulation; the posterior umbonal 

 slope is also marked, immediately below the margin of the escutcheon, by 

 a slightly concave sulcus, across which the undulations are more faintly 

 marked than below. 



The species is closely allied to Allorisma clavata, McOhesney, 

 and was at first supposed to be identical ; but on comparison, 

 it shows so many points of difference that it became necessary to 

 consider it as a distinct species. 



Formation and Locality. — In limestone of the age of the 

 Chester group (or Chester and St. Louis combined), at Newton- 

 ville, Ohio. Collected by Prof. E. B. Andrews, to whom the 

 species is dedicated. 



Allorisma ITIaxviilensis, u. sp. 



Pal. O., Vol. Ill, Plate 10, Figs. 7 and 8. 



Shell small, the specimen used being a little less than one inch in length, 

 and the height less than half the length. Form of the shell transversely 



