482 



NORTH AMERICAN INDEX FOSSILS. 



LXXXIX. Schizodus King. 



Shell thin, ovate, often tending toward quadrate, longest pos- 

 teriorly. Right valve with two teeth ; left with three. Surface 

 marked with concentric striae or nearly smooth. Muscular im- 

 pressions two ; the anterior with a small radial buttress. Pallial 

 line simple. Devonic-Permic. 

 318. S. chemungensis (Conrad) (S. appressus Conrad). (Fig. 



642, b.) Devonic. 



Surface covered with fine concentric striae which often strengthen 

 into varices near the base. 



Hamilton : New York. Chemung : New York, Pennsylvania. 



Fig. 642. a, Schizodus qnadrangularis ; b, S. chemungensis ; c, S. gregarius ; a, 

 S. rhombeus. All left valves. (N. Y. Surv. ) 



319. S. gregarius Hall. (Fig. 642, c.) Devonic. 

 Distinguished by its small size and elongate form. 

 Chemung Group : Pennsylvania. 



320. S. rhombeus Hall. (Fig. 642, d.) Devonic. 

 Distinguished by its nearly quadrate form. Below the medium 



size but larger than 5. gregarius. 



Chemung Group : New York, Pennsylvania. 



321. S. quadrangularis Hall. (Fig. 642, a.) Devonic-Carbonic. 

 Differs from S. chemungensis in its more quad- 

 rate form and more nearly central beaks. 



Chemung Group : New York. Waverly : 

 Ohio. Coal Measures : Pennsylvania. 



322. S. medinaensis Meek. (Fig. 643.) 



Mississippic. 

 Subtrigonal. Surface nearly smooth. 

 Waverly : Ohio, Indiana. 

 323. S. cuneatus Meek. (Fig. 644.) Mississippic-Carbonic. 



Fig. 643. Schizo- 

 dus medinaensis. 

 (Ohio Pal., II.) 



