690 GEOLOGICAL SURVEY OF IOWA. 



Acrocrinus nriwforiaiis ( n. s.). 



PLATE XXV. FIG. 9 a, b. 



BODY small, with base divided on one side, very symme- 

 trically urnshaped, gradually swelling out from the rimlike 

 base with the sides very gently curving, preserving on the 

 most extended portions about ten ranges of plates which are 

 irregularly pentagonal or hexagonal. 



Arms and column unknown. 



This species has the same geological associations as the A. sjiumardi described by 

 Dr. YANDELL. 



Geological formation and locality. In the Kaskaskia limestone : Pope 

 county, Illinois. 



Pentremites cervinus ( n. s.). 



PLATE XXV. FIG. 11 a, b. 



BODY angularly subovoid ; the base, below the pseudo- . 

 ambulacral areas, three-fourths as long as the part above, 

 obtuse, the basal plates forming a little prominence not 

 sloping in the same plane as the succeeding ones : section 

 across the body, at base of pseudambulacral areas, pentangu- 

 lar, with the sides slightly concave ; sides sloping somewhat 

 abruptly from the greatest diameter to the summit. Basal 

 plates forming a shallow pentagonal cup with the angles 

 highly elevated, and each plate sometimes a little protuberant 

 just without the column-area. Radial plates broad below and 

 abruptly diverging to the base of the pseudambulacral areas, 

 the width at base and summit very nearly equal. Interradial 

 plates long lanceolate, reaching to within the width of three 

 or four poral pieces of the ovarian openings. 



Pseudambulacral areas limited by the elevated margins of 

 the forked radial plates, slightly convex near the exterior 

 margin, and thence sloping gently to the median line, very 

 gradually expanding in width to the summit, marked by 

 about fifty (more or less in specimens of different age) pore- 



