r^2 TRANS. ST. I-OUIS ACAD. SCIENCE. 



Body ovoid, having its greatest diameter a little above the cen- 

 tre of the calyx. Pelvis very small, not depressed ; its diameter 

 is equal to about three times the thickness of the column ; exter- 

 nally ornamented w^ith granules running parallel to the sutures. 

 Fork-pieces long ; sinus for the reception of the ambulacral field 

 as long as four-fifths of its entire length, being wider in the begin- 

 nino- than towards the apex, with a little crest in the centre of its 

 base portion. Deltoid pieces small, lateral expansion as long as 

 one-fifth of the entire body, externally ornamented with large and 

 small granules arranged in a rosette shape, and a flat raised tri- 

 angular surface near the mouth. Ambulacral field extending 

 nearly over the entire surface of the body, with a comparatively 

 deep groove in the centre, being wider in the beginning than 

 toward the apex. Lancet pieces half as wide as the sinus. Poral 

 pieces comparatively small, numbering nine in one-tenth of an 

 inch. Mouth central ; ovo-spiracle apertures very small, each iso- 

 lated, except two which adjoin the anal opening, being situated 

 at the beginning of the flat triangular surface. Interambulacral 

 .space ornamented by alternating broad and small transverse pli- 

 cations running almost horizontally along the margin of the am- 

 bulacral field, leaving in the centre a lancet-shaped depression 

 which is ornamented with fine longitudinal granulated lines. 



Dimensions — Vertical height about one-fifth more than the great- 

 est transverse diameter. 



Geological formation and locality — In the Chouteau limestone in 

 Pettis Co., Missouri. 



I dedicate this fine species to the lucky finder, my friend, 

 Mr. F. A. Sampson, of Sedalia, Missouri. The specimen is in 

 his collection. 



For better comparison and to show the difference between it 

 and allied species, I have given also the figures of the original 

 specimens of Pentremites Rcemeri Shumard (pi. D, figs. 3, 3a) 

 and Pentremites granulostis Meek and Worthen (pi. D, figs. 4, 

 4a), of which the original specimen was kindly loaned to me by 

 Prof. A. H. Worthen. 



