Hamhach — Reoisioyi of the Blastoideae. 57 



lacra concave, broad, leaf -like, and sunk so that the surface 

 does not reach the upper margin of the sinus. Interambu- 

 lacral area not so depressed as in Pentremites siilcatiis^ with a 

 very prominent and coarsely serrated margin at each side of 

 ambulacrum from the base of the sinus to the deltoid suture. 

 External deltoid surface rather convex, smooth, with a sharp 

 prominent base point, projecting much over the summit. 

 Whole surface finely striated. Poral pieces 9 to J inch. 

 Genital openings as in Pentremites sulcatus. All my specimens 

 vary from J to IJ inches in diameter. Transverse diameter 

 one-fourth greater than the vertical diameter. The serrated 

 edge of each side of the ambulacrum distinguishes this species 

 readily from Pentremites sulcatus^ its nearest ally. 



The geological formation is the Chester limestone, but I 

 have never found it at Chester or Evansville, Illinois, or 

 around there. It occurs at Ste. Genevieve, Missouri, and at 

 Baldwin, Illinois. 



Cribkoblastus incisus n. s. 



Plate v., Fig. 2. 



Body globose, of medium size, seldom more than f inch 

 in diameter. Base very small, depressed, not visible in a 

 lateral view. Ambulacrum narrow, linear, running almost 

 over the whole surface of the body. Deltoid pieces very 

 small, visible externally, but entirely confined to the summit. 

 Interambulacral area convex and granulated, with a deep 

 suture in the center and a lunary impression at each side of 

 the ambulacral margin, dividing each side of the ambulacral 

 sinus in two ; and a little spine-like projection at the apex of 

 the sinus readily distinguishes it from C . melo and other allied 

 forms. Genital openings very small but not confluent with 

 each other. 



Geological formation and locality: Lower Burlington lime- 

 stone, Burlington, Iowa. 



