117. CONTRIBUTION TO 



this form to P. cherokeus, but not without some doubt, however, as to the 

 validity of the species. 



There seem to be few dilf'erences of no importance, between P. cherokeus 

 and P. sulcatus. if Hall and others have correctly identified them. There is a 

 larger form than either from Tennessee, and said to occur in the St. Louis Lime- 

 stone, which may, after all, be the form originally referred to P. cherokeus by 

 Troost. 



Tlie specimen under consideration has a strongly convex base, with an 

 almost straight edge from tlie distal end of the ambulacrum to the columnar 

 base. The deltoid is less than one-fourth as long as the ambulacrum, and pro- 

 jects upward into a spine-like process. The ambulacra form broad troughs, 

 bordered by the rather deep, sharp edges of the fork pieces, the latter being 

 crimped as mentioned in the description of P. obesus. The ambulaeral fields 

 form strong folds below, or the body is strongly five-lobed -at the ambulaeral 

 tips. 



The central ventral opening is a small five-pointed star. The spiracles are 

 almost round, while the anal opening is somewhat elliptical. 



Collected from the Kaskaskia Limestone at Clifty Station, Grayson 

 count3^ Ky. Collection of Mr. G. K. Grt ene. 



P E N T R E M I T E S C H E S T E R E N S I S , Hambach, Rowley. 



Plate 36. Figs. 7, 8, 9, 10-11. 



The specimen figures 7 and H differs in some minor details from Dr. Ham- 

 bach.'s description of the type, the basal portion of the body to the lower ends 

 (tf tlie ambulacra being proportionally much greater in depth in our specimen, 

 the basal cup itself being deeper, and that part of the fork piece below the tip 

 of the ambulacrum sloping strongly toward the basal cup instead of being 

 nearly horizontal as in /-*. r/teJite/'e/i.iLs. 



The ambulacra are rather medium in width, nearly flat, and but little 

 below the interambulacral surface. 



The entire specimen has a somewhat double conical shape, the interambu- 

 lacral fields being nearly flat and the greatest width of body being at the distal 

 ends of the ambulacra. 



Tlie deltoids area little nuM-e than one-third of the length of the ambulacra, 

 but tiieir proximal ends do not extend (juite to the summit, while in /\ cheato'- 

 cii\'>fi they extend above. 



The test is rather thi:;. No surface ornamentation is visible on our speci- 

 m e-n . 



