656 GEOLOGICAL SURVEY OF IOWA. 



Pentremites koninckana. 



PLATE XXII. FIG. 11 a, b, c. 

 Pentremites koninckana : HALL, Transactions of the Albany Institute, Vol. iv, 1856. 



BODY small, globose or subpyriform, upper part rounded ; 

 base subpyramidal, angular. Basal plates small, the lateral 

 edges short and covered by the column, allowing the base 

 of three of the radial plates to come within the limits of the 

 column-area; the two other plates resting upon the long 

 sides of the larger basal plates. Radial plates short, convex 

 in the middle and sloping to the sides, widening a little from 

 the base upwards, and dividing only half way down for the 

 reception of the pseudo-ambulacral areas. Interradial plates 

 minute, linear or tapering very gradually upwards to a point, 

 and having two extremely short oblique sides below. Pseudo- 

 ambulacral areas broad, nearly plane, and extending only 

 about half way from the summit to the base, rather deeply 

 impressed at their rounded lower ends. Poral plates varying 

 from six to thirteen. Oral aperture small, pentagonal : anal 

 aperture large, oval ; ovarian openings small, nearly round. 



SURFACE very finely and beautifully striated : striae on the 

 sides of the radial plates nearly vertical, but on the lower 

 part deflected obliquely across so as to meet at an obtuse 

 angle on the centre below the ambulacral areas. 



COLUMN, at its' junction with the body, round, relatively 

 very large. Length, one-twelfth to one-fourth of an inch. 



This species resembles P. caryophyllatus of DE KOHTINCK ( Crinoides du Terrain 

 carbonifere de la Belgique), but differs in the shorter base and peculiarity of the 

 basal plates, as well as in the interradial plates, which in our species are extremely 

 small and almost linear, the one on the anal side extending into that aperture. A 

 single individual shows a nearly entire obliteration of one of the pseudo-ambulacral 



spaces. 



Fig. 11 a. A specimen, natural size. 



Fig. 11 b. The same enlarged. 



Fig. 11 c. Summit of the same enlarged. 



Geological formation and localities. In limestone of the age of the War- 

 saw limestone : Spergen hill and Bloomington, Indiana ; and Alton, 111. 



