PELECYPODA—PRIONODESMACEA. 



449 



232. A. subdecussata Hall. (Fig. 591, b.) Devonic. 

 Beak nearly terminal. Ear very small, limited by a vertical 



furrow. Surface marked with alternating strong and weak, sub- 

 angular rays crossed by concentric striae. 

 Hamilton : New York, etc. 



233. A. decussata Hall. (Fig. 591, c.) Devonic. 

 Differs from A. subdecussata in the greater and nearly equal 



convexity of the two valves, in the broader furrow at the anterior 



Fig. 592. Aclinopteria boydi. (Pal. N. Y., V.) 



ear, and in the stronger rounded rays and their interruption by 

 the concentric lamellae. 



Hamilton : New York, Pennsylvania. 



234. A. boydi Conrad. (Fig. 592.) Devonic. 



Differs from A. subdecussata in the less defined furrow at the 

 anterior ear, the less obliquity and broader body of the shell, and 

 in the rays being practically of one size. 



Abundant in the Hamilton : New York, Pennsylvania, Indiana, 

 Ontario. Portage : New York (characteristic). Lower Devonic 

 of Nevada. 



LXXI. Ptychopteria Hall. 



Differs from Actinopteria in the pointed anterior extremity and 

 large, straight wing marked by a strong longitudinal fold. Hinge 

 line linear, with one or two linear oblique cardinal and lateral 

 teeth. Surface marked with fine rays. Devonic. 



