488 NORTH AMERICAN INDEX FOSSILS. 



Hamilton : New York, Ohio, Kentucky, Indiana, Michigan. 



335. A. scabridus Hall. (Fig. 650,/.) Devonic. 

 Differs from A. princeps in its very obtuse angle at the hinge 



line, and especially in the imbricating growth lines which usually 

 form short, almost tubular spines when passing over the rounded 

 rays. 



Hamilton : New York. 



336. A. striatus Hall. (Fig. 650, d.) Devonic. 

 Small ; surface including ears covered with fine regular and 



closely arranged rays. 



Chemung : New York, Pennsylvania. 



337. A. duplicatus Hall. (Fig. 650, a.) Devonic. 

 Beaks obtuse, prominent. Ears small. Surface including ears 



covered with regular duplicating rays crossed by fine concentric 

 striae ; umbo nearly smooth. 



Chemung : New York, Pennsylvania. 



338. A. cancellatus Hall. (Fig. 650, e.) Devonic. 

 Height slightly greater than length. Lateral margin of anterior 



ear rounded. Surface including ears marked with fine rays crossed 

 by fine striae, giving the shell a cancellated appearance. 

 Chemung : New York. 



339. A. caroli Winchell. (Fig. 650, c.) Mississippic. 

 Differs from A. striatus in its more circular form, obtuse beak, 



and stronger radii. 



Waverly : Ohio, Iowa. 



340. A. coxanus Meek and Worthen. (Fig. 651.) Carbonic. 

 Radiating ribs alternating in size, the smaller ones 



dying out before reaching the hinge. Concentric striae 



fine and close. 



Coal Measures : Pennsylvania-Oklahoma and Ne- 



_ , braska. 



Fig. 651. 



Avicuiopecten 34 1. A. rectilaterarius (Cox). Carbonic. 



coxanus. Height and length about equal (about | inch). An- 



VI/lA ' ter * or ear separated by an indistinct furrow from body 



of shell. Posterior ear not defined, large. Posterior 



margin nearly straight. Radiating striae somewhat rib-like, crossed 



by concentric lines. Differs from A. coxanus in its slightly larger 



size ; larger posterior ear and straight posterior border. 



