38 BULLETIN OF THE LABORATORIP.S 



mens much less transverse and with distinctly alternate stride occur. 

 In the free-stone this form occurs with var. cylindrica (=r var. robusta, 

 Hall), which latter, or a still more Orthis-like variety, occurs in 

 congl. II. 



Orthis Vanuxemi. Hall, var. pulchellus, 



(Plate V, Fig. 9.) No. 1396. 



This beautiful little Orthis occurs in large numbers in a zone near 

 the top or above the top of the quarry rock in Granville, and seems 

 to pass into forms resembling those generally identified with O. mi- 

 chelina. Without discussing the probable relationships of the two forms 

 we may simply notice the close resemblance of our specimens to those 

 described by Prof. Hall, from "calcareous shales of the age of the 

 Hamilton group" in several localities in Illinois, Missouri, Iowa, and 

 New York. 



Shell nearly circular or sub-qu idrate in outline, depressed, ven- 

 tral valve generally longer than wide, most convex one-fifth from the 

 beak, flattened, but not sinuous below. Hinge line short ; beak rather 

 prominent, protiuding, acute; ears depressed, rounded. Surface cov- 

 ered with numerous small, tubular striae which increase by bifurcation 

 or more rarely implantation, sometimes by division into three, striae 

 with porforations or oval punctures ; surface also marked by concentric 

 striae and more distant imbricating lines especially near the front mar- 

 gins ; about three stria in the space of one millimeter. Foramen with 

 cardinal process ; interior of valve with large vascular impression, and 

 mesial process. Dorsal valve nearly circular, convexity above the 

 middle, cast with a broad mesial sulcus from the beak to near the mid- 

 dle. Length of ventral valve 15 mm; width i^ mm. 



Orthis michelina, var. burlingtonensis, H-, is hardly at all differ- 

 ent. In it the perforations upon the striae are represented as elongate 

 rather than circular, in which point our specimens agree. 



More typical specmiens of O. michelina also occur in the free- 

 stone. 



