24 



sal valve broadly convex, beak broad, closely incurved, umbonal parts 

 a little flattened. 



Surface marked by eight or ten simple, somewhat angular plica- 

 tions, which are visible only on the front part of the shell ; two of 

 these are depressed on the ventral valve for the mesial sinus, the 

 tongue of which, in the older specimens, is considerably elevated ; the 

 mesial fold has three plications, and is slightly elevated at the front ; 

 the plications on each side of the mesial fold and sinus are usually 

 indistinct. Nearly half the length of the shell from the beaks is free 

 from plications, and only marked by fine concentric lines of growth, 

 so that the half-grown specimens present very little appearance of a 

 plicated shell. Shell structure distinctly fibrous. 



Locality and position, in the St. Louis Limestone at Ottumwa, and 

 near Oskaloosa, Iowa. 



Genus Spirifer Sowerby. 



Spirifer glans cerasus (n. s.) Shell very small, globose, subcir- 

 cular in outline, front border slightly emarginate, hinge line less than 

 the width of the shell ; ventral valve with a rather broad, faintly-im- 

 pressed sinus ; beak high, arcuate, incurved ; area narrow, indistinctly 

 defined ; foramen about as wide as high. Dorsal valve somewhat 

 regularly convex, without a distinct mesial fold ; umbo rather promi- 

 nent; beak small, prominent, and projecting a little back of the hinge 

 line. Surface marked by concentric lines of growth, but no radi- 

 ating striae, or ribs, have been observed. 



This species is of the type of S. lineatus of Martin, but differs 

 from that species, as identified in our Coal Measures, by its more cir- 

 cular and globose form, shorter ventral beak, and less convex dorsal 

 valve. From the young of S. diibius of Hall, with which it is asso- 

 ciated, it differs in its much more globose and circular form, higher 

 area, and more prominent ventral beak. 



Locality and position, in limestone of the age of the Hamilton 

 group of New York, Iowa City, Iowa. 



Observations on the 



Genus Spiriferina D'Orbigny. 



In the Chemung and lower carboniferous rocks of the West, are 

 several species of shells which have been referred to the genus Spirifer, 

 which probably ought to be referred to Spiriferina. One of these, 

 S. spinosa of Norwood and Pratten, possesses all the characters of 

 Spiriferina, — the punctate structure, spinulose surface, pseudo-deltid- 

 ium, and internal septum, — and was referred to that genus by 

 Prof. Hall, in 1856. Spirifer solidiroAtris White has the punctate 

 structure, internal septum and pseudo-deltidium of Spiriferina, but is 



