56 Trans. Acad. Sci. of St. Louis. 



Pentremites bradleyi Meek. 



Plate v., Fig. 7. 



TBodv small, obtuse, conical. Basal portion almost flat, and 

 resembling that of Pentrevmtes conoideus very much, but be- 

 ing more rounded and having a larger articulation surface for 

 the column, in proportion to its size, than Pentremites 

 conoideus. Ambulacra broad, excavated along the middle, 

 and having rather narrow integumental plications, there being 

 about twelve to one-eighth of an inch. Deltoids visible 

 externally. Genital openings as in all true Pentremites. 



This species was first described by Meek, but merely in a 

 foot note, comparing it with Pentremites koninchiana = 

 conoideus Hall. It differs from Pentremites conoideus in being 

 more obtuse, with broader and more deeply excavated ambu- 

 lacra than Pentremites conoideus, in which the ambulacra are 

 narrow, more rounded, and the surface plications coarser. 

 The interambulacral spaces are depressed more in Pentremites 

 conoideus than in this species. It differs from Pentremites 

 godoni in being not as round, with more depressed ambulacra, 

 and in not having the sharp crest-like margin around the 

 sinus. 



Geological formation and locality : Subcarboniferous on 

 the Divide between Ross Fork and Lincoln Valley, Montana. 

 First mentioned in F. V. Hay den's Sixth Annual Report of 

 the United States Geological Survey of the Territories, 1872, 

 p. 470. Types in the Smithsonian Collection, numbered 

 24,529. 



Pentremites serratus n. s. 



Plate IV., Fig. 9. 



Body rol)ust and resembling Pentremites sulcatus very much. 

 Base flat and disk-like, showing a distinctly triangular depres- 

 sion around the articulation surface of the column. Ambu- 



