452 PALMONTOLOGY OF NEW YORK. 



SCHIZOUUS OREGARIUS. 



PLATE LXXV. FIGS. lG-18 ; AND I'LATK XCV, FIG. 27. 



SehiziHlit.t gregariux. Hall. Pi-elira. Notice Lamellibranchiata, 2, p. 97. 1870. 



CythiTodon (Sdiizoiiux) gi-t-ffarivx. Hall. Piil. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 75, 



tigs. 16-18. 1883. 



Shell small, sub-rhomboid-ovate, sometimes sub-cuneate from compression ; 

 length from one-fourth to one-third greater than the height ; basal margin 

 regularly and broadly curving. Posterior extremity somewhat pointed 

 below and obliquely sub-truncate above. Cardinal line short, less than half 

 the length of the shell. Anterior end short, broadly rounded. 



Valves moderately convex below, becoming somewhat gibbous in the mid- 

 dle and above. 



Beaks at about the anterior third, small, rising little above the hinge-line. 

 Umbonal slope obtusely sub-angular, continuing to the post-inferior extremity. 



Surface marked by fine concentric striae. 



Two specimens measure respectively 12 and 15 mm. in length, and 9 and 

 12 mm. in height. 



This species is similar in form to 3'oung individuals of S. appressus, but is 

 proportionally longer. It is also smaller and proportionally longer than speci- 

 mens of iS. rhombeus. 



Formation and locality. Abundant in some chocolate-colored, sandy shales of 

 the Chemung group, on the banks of the Tioga river, near Covington, Pa. 



SCHIZODUS RHOMBEUS. 



PLATE LXXV, FIGS. 19-23. 



C'ypricardiaf rhombea. Hall. Geol. 8urv. N. Y., Rep. Foui-th Dist., p. 291, t. 139, figs. 2, 3. 1843. 

 {•Icfiizodux rhmnlieim, Hall. Prelim. Notice I^amellil)ran<;hiata, 2, j). 97. 1870. 



CijlJurndini (.S'cAizorfw) rhiinlM'Un, Hall. Pal N. Y., vol. v, jit. 1. Plates and Explanations: PI. 75, 



figs. 19-23. 1883. 



Shell below the medium size, sub-rhomboidal ; length a little greater than the 

 height ; margins regularly rounded from the anterior end to the post-inferior 

 extremity. Posterior extremity truncate. Cardinal line short. 



