PALEONTOLOGY OF IOWA. 695 



PLATE XXV. FIG. 15. 

 Pentremites obesiis : LYON, Report on Geology of Kentucky, 1857, pa. 469, pi. 2, f. 1 a-d. 



BODY angularly ovoid, its greatest diameter below the centre, 

 width about three-fourths of the height. Basal plates longer 

 than wide, forming altogether a pentapetalous cup. Radial 

 plates narrowed below, obtusely angular along the middle 

 to the base of the ambulacral areas, where they are extreme- 

 ly prominent ; the bifurcation extending for three-fifths the 

 length of the plate. Interradial plates long lanceolate. 

 Pseudambulacral areas long and narrow, extending two-thirds 

 the entire length of the body, concave in the middle, having 

 the appearance of a rounded groove along the median line, 

 convex near the outer margin, and each side divided by a 

 longitudinal suture ; along which line the plates are fre- 

 quently separated, showing the area to be distinctly com- 

 posed of four ranges of plates. The number of plates in the 

 length of the area varies from ninety to more than one 

 hundred ( 43 in the young to 150 in full-grown specimens, 

 LYON). The mouth is acutely pentangular; the ovarian aper- 

 tures broad ovate or rounded. 



This species has been very elaborately described and illustrated by Mr. LTON in 

 the report cited above. 



Fig. 15. Lateral view of a specimen, natural size. The species frequently attains a 

 larger size. 



Geological formation and localities. In the Kaskaskia limestone : Southern 

 Illinois, and Kentucky. 



Pentremites globosus. 



PLATE XXV. FIG. 17, 

 Pentremites globosus : TROOST, MS. of Monograph. 



BODY globose, small : base rounded or subangular, short, 

 greatest diameter about the centre. Interradial plates not 

 reaching the summit. Pseudambulacral areas comparatively 



