60 Trains. Acad. Sci. of St. Louis. 



length of the piece. Margins of the sinus drawn out to form 

 a prominent crest on both sides of the ambulacrum, thus 

 causing the interambulacral space to be slightly concave. 

 Deltoids small, the upper portion running out to a small 

 projecting spine. Summit openings, i. e., mouth, anus and 

 genital openings, twelve in number and not confluent. 



This species, which resembles O. cornutus Meek and Wor-- 

 then, diifers from it, however, in the following characters : 

 The base is not depressed as much, the margins of the ambu- 

 lacral sini are less prominent, and the interambulacral spaces 

 are not excavated as much as in (7. cornutus. The interam- 

 bulacra are twice as wide as in G, cormutus, in which species 

 the interambulacra are about as wide as the ambulacra. The 

 spiny projection is not as long or as prominent as in C. 

 cornutus. Besides the foregoing differences the surface orna- 

 mentation is different in the two species, being granular in 

 C. cornutus, and finely striated in the species under consider- 

 ation. 



Geological formation and locality: Subcarboniferous. 

 Divide between Ross Fork and Lincoln Valley, Montana. 

 The specimens were collected by Hay den's party, and first 

 mentioned in the Annual Report for 1872, page 470, un- 

 der the name Pentre7nites hradleyi, Meek. Types in the 

 Smithsonian Collection, numbered 24,529. By close exami- 

 nation it was found that the specimens under this number con- 

 sisted of two different species, one of these I have here named 

 in honor of mv friend, C. Schuchert. 



Saccoblastus ventricosus, n. s. 

 Plate IV., Fig. 7. 



Body bipyramidal. Base cup-shaped, with three charac- 

 teristic impressions peculiar to this genus. Articulation sur- 

 face of the column triangular. Column triangular. Ambu- 

 lacrum very narrow, linear and sunk into the very prominent 

 ambulacral sinus. Interambulacrum smooth and dipping a 

 little toward the fork piece suture. Genital openings near 



