25 



not spinulose. Spiriferina ? suhtexta, herein described, has the inter- 

 nal septum and punctate structure, but our specimens do not show 

 the pseudo-deltidium, and the species is destitute of spines. A single 

 ventral valve from the Lithographic Limestone of Clarkesville, Mo., 

 probably referable to the latter species, shows the interior septum, 

 but no other definite character of Spiriferina. 



The punctate structure of the shell in all these species is coarser 

 than is usual in Terebratula Retzia, &c., and is hardly distinguishable, 

 except in weathered and exfoliated conditions. The outer layer, and 

 lamellfe, appear not to possess this character, and to hide that of the 

 substance beneath, so that it does not appear in the better preserved 

 specimens. The pseudo-deltidium might easily have been removed 

 from S. suhtexta, while S. solidirostris is known to possess it. Thus 

 these two species, doubtless, possessed all the characters of Spiriferina, 

 except the spinulose surface ; and, as this latter character is consid- 

 ered of only specific importance in some other genera, these two 

 species are referred with a query to that genus. 



Spiriferina ? subtexta (n. s.) Shell rather small, subglobose, 

 hinge line varying in length from less than the width to the greatest 

 width of the shell. Dorsal valve subsemicircular in outline, somewhat 

 regularly convex, umbonal parts rather prominent, beak small, in- 

 curved over the hinge line. Ventral valve deeper than the other, arcu- 

 ate from beak to front, area large, not distinctly defined on its upper 

 margins ; foramen narrow, reaching to the beak, which is acute, and 

 incurved ; five or six prominent plications on each side of the mesial 

 fold and sinus ; sinus moderately large, distinctly defined to the beak ; 

 mesial fold scarcely raised above the general convexity of the shell 

 except at the front ; the ribs bordering the sinus, and the depressions 

 bordering the mesial fold, larger than the others. 



Surface marked by fine concentric lamellae of growth, which are 

 most conspicuous near the front margins. Shell structure conspicu- 

 ously punctate, when exfoliated or much weathered. 



This species most nearly resembles Spirifer (Spiriferina f) solidiros- 

 tris White, but differs in its more globose form, less number of ribs, 

 higher area, and having its foramen open to the beak. 



Locality and position, in the upper and lower divisions of the Bur- 

 lington Limestone, Burlington, Iowa. 



Genus Cyrtia Dalman. 



Cyrtia curvilineata (n. s.) Shell rather small, greatest width 

 forward of the hinge line ; ventral valve much elevated ; beak small, 

 more or less incurved, and pointing backward beyond the cardinal 

 border ; the sloping sides of the area about equalling the length of 

 the hinge line ; deltidium forming an elliptic arch over the foramen. 



