212 



oligoptycha differs from this species in the proportionally 

 longer hinge line, and when compared with specimens of Sp. 

 macropleura from Tennessee presents no essential differences. 



Spirifer crispus (var.) 



This species occurs in considerable numbers in the Wal- 

 dron collections, presenting the same variety of form and 

 proportions that we find in the species from New York. 

 Many of the specimens however, are larger and more rotund 

 than those from the latter locality. 



There are numerous small symmetrical specimens which 

 have almost uniformly a single plication on each side of 

 the mesial fold, presenting three folds of nearly equal size. 

 The ventral valve has two folds on each side of the mesial 

 sinus, while the valves are almost equally convex. The 

 surface is marked as in the larger specimens. 



There seems to be no sufficient reason for separating this 

 form from Sp. crispus. The Sp. quadricosta of vol. 2, Pal. N. F. 

 is probably identical with these, but found in a different 

 condition of preservation. 



GENUS MERTSTELLA (Hall.) 



Meristella Maria (Hall). 



Shell of medium or large size, ventricose, broadly ovate 

 or sub-quadrangular. Ventral valve gibbous above, with 

 a sub-angular ridge extending from the beak to near the 

 middle where it becomes flattened and sinuate, and bent 

 abruptly upwards in a prolonged linguiform extension ; 

 beak obtuse, closely incurved over the opposite valve ; 

 cardinal slopes angular, and the cardinal border inflected. 

 Dorsal valve gibbous, strongly arcuate transversely, pro- 

 minently sub-angular along the middle, and in the lower 

 part becoming a broad uudefined fold, deeply emarginate 



