706 GEOLOGICAL SURVEY OF IOWA. 



Spiriler spinosus. 



PLATE XXVII. FIG. 5 a, b, c. 



Spirifer spinosus : NORWOOD & PRATTEN, Transactions of the Academy of Nat. Sciences, 



Philadelphia, 1856, pa. 71, pi. ix, f . 1 a, 6, c, d. 



SHELL less than the medium size, semioval : cardinal 

 extremities equalling or greater than the width of the shell 

 below, gibbous in the middle. Dorsal valve a little shorter 

 than the opposite ; mesial fold prominent, and defined on 

 each side by a deeper furrow. Ventral valve slightly more 

 convex than the opposite ; mesial sinus strongly defined ; 

 beak slightly arched ; cardinal area moderately high, a little 

 less than the width of the shell : foramen moderate. 



SURFACE marked by four or five angular plications on each 

 side of the mesial fold and sinus, which are marked by con- 

 centric imbricating lamellae of growth : entire surface finely 

 punctate, with numerous small tubular spines irregularly 

 distributed. 



In its punctate surface this shell resembles S. kentuckensis of SHTJMARD, but differs 

 in being more robust, in the coarser punctse or granulations, and in the presence of 

 the tubular spines. 

 Fig. 5 a, b. Dorsal and ventral views of this species. 



Fig. 5 c. Enlargement of the surface, showing the punctate character of the shell and 

 the bases of the small spines. 



Geological formation and localities. In the Kaskaskia limestone : Kas- 

 kaskia and Chester, Illinois ; Crittenden county, Kentucky. 



Spirifer increbescens ( n. s.). 



PLATE XXVII. FIG. 6 a - i. 



SHELL transversely semioval, gibbous : hinge-line equal- 

 ling the greatest width of the shell, and terminating in more 

 or less salient submucronate extensions which are frequently 

 unequal on the two sides of the shell. Dorsal valve gibbous 

 in the central and umbonial parts, and becoming depressed 

 and somewhat flattened at the cardinal extremities ; mesial 

 fold simple at the apex, bifurcating just below the beak and 

 again on the umbo, making four plications, which are rounded 



