44 BULLETIN OF THE LABORATORIES 



lie at least sixty feet below congl. 1. Shell nearly semi-circular ; mod- 

 erately convex; length 4-3-2 >^ times the height; valves of nearly 

 equal convexity. Hinge-liiie considerably extended with acute ears, 

 which are sometimes mucronate. Ventral valve convex with a rather 

 prominent beak and strongly curved striated area; greatest convexity 

 near the beak ; lateral portions depressed; sinus narrow, but rather 

 deep; surface marked by 40 rounded plicas which are dichotomous, 

 and of which about four occupy the sinus, which is triangular m sec- 

 tion, especially near the beak. Area moderately narrow and strongly 

 inclined, with a broad triangular area which is striate. Dorsal valve 

 only moderately convex, laterally depressed, most convex above the 

 middle, fold very inconspicuous, scarcely elevated, with two pairs of 

 plicae produced by bifurcation of the two primary ones. Dichotomy 

 of strice of both valves very irregular. Surface concentrically striate, 

 sometimes with concentric folds also. Found in the lowest horizon of 

 Licking Co. Its range being 20 feet, so far as observed. 



This species was first described from the so-called Chemung of 

 Missouri. Later, Prof. Hall, in his Iowa Report describes specimen 

 from rocks of the Hamilton age, while Prof. Winchell noted its occur- 

 rence in Waverly strata, at Sciotoville, O. 



The casts show peculiar internal structures which may be of 

 assistance in destinguishing the species. 



Spivifer stvi(ltiforn^is,'^^^^^^ 

 {^\■^iiQ III, Fig. 26; Plate VI, Figs. 6-7.) 



Undoubted and typical specimens. are found in our upper Waver- 

 ly, well toward the summit of the series. The illustrations in the third 

 volume of the Ohio Palaeontology convey a good idea of this shell. 

 Isolated dorsal valves, however, resemble the shell called in Ohio, S. 

 carteri, and are sometimes so-called. Eight to twelve plicae occupy 

 the mesial fold. The fine radiating striae, when preserved, are good 

 specific marks. 



Shell of medium size ; semi-oval in outline, only moderately con- 

 vex mesially, rather flat toward the sides; hinge-line equal to greatest 

 width or sometimes less, ofien slightly mucronate ; lateral margins 

 generally making with the hinge-line about a right angle. Ventral 

 valve much more convex than the dorsal; beak strongly incurved; 



