292 



NORTH AMERICAN INDEX FOSSILS. 



the beak concave. Surface bearing numerous (20-26) low, rounded, 

 simple plications of which six and five (sometimes 8 and 7) occupy 

 respectively the fold and sinus. 



Helderbergian (Coeymans) of New York. 



Fig. 361. Uncinidus mutabilis (Pal. N. Y., III.). 



269. U. abruptus Hall. (Fig. 362.) Devonic. 



Transversely oval. Pedicle valve depressed-convex and very 

 abruptly deflected (almost at a right angle) toward the opposite 

 valve on the lateral and anterior margins; beak small, closely in- 

 curved. Brachial valve very prominent in front; beak depressed. 



Fig. 362. Uncinidus abruptus (Pal. N. Y. 



Surface with 25 to 33 simple, subangular plications ; the low but 

 distinct fold and sinus occupied by about 7 and 6 respectively. 

 Helderbergian (New Scotland) of New York. 



