246 Messrs. H. Etlieridge, Jun., and P. H. Car])enter on 



is so large as to remove all trace of the broad median ridge 

 separating the two spiracles at the sides of the corresponding- 

 oral plates ; and the lateral tubes are therefore fused with the 

 anus into one large anal spiracle — a character which increases 

 the resemblance between the summit-structure of this species 

 and that of Pejitremifes proper. Except in 8. melo, the spiracles 

 of Schizohlastus are at the sides of the proximal side plates, 

 whilst those of Pentremites are between the latter and the 

 mouth. 



We have not succeeded in ascertaining whether or not the 

 lancet-plate is double, as in Pentremites ; but we believe that 

 it is not. In S. Hayi it is undoubtedly traversed by three 

 canals, one being that of the ^vater-vessel. The nature of the 

 other two is not at present clear to us ; but we hope to discuss 

 the question fully in our larger work. The side plates in 

 Schizohlastus rest on the lancet-j)late, ])artially hiding it from 

 view, and not simply against it as in Pentremites. 



It is scarcely visible in S. inelonoiclesj S. 2}isitmj and S. neg- 

 IcctuSj rather more exposed in ^S'. melo, and still more so in 

 S. Sayij in which it occupies the median third of the ambu- 

 lacrum. The side plates vary from about twenty to eighty 

 in number on each side of the ambulacrum. They number 

 about twenty-six in S. ^^ifton, from twenty-tive to thirty in S. 

 iierjlectusj 8. glaher^ and 8. gramdosus^ and eighty in 8. 8aiji. 

 Outer side jilates are unknown in 8. melonoidesj 8. lyisuin, 8. 

 neglectusj and 8. gJaber. 



We are acquainted with the number of hydrospires in only 

 8, 8ayi, in which there are four on each side. 



Not unfrequently a sulcus of variable depth occurs on each 

 side the ambulacra, between the ends of the side plates and 

 the edges of the radial sinuses. The ambulacra are either 

 on the same level with the general surface of the calyx, as in 

 8. 8ayi and 8. projeclus^ or a little below it, as in 8. granu- 

 losus. 



The surface of the plates in 8cJ/izohIastiis is usually highly 

 ^ornate; but 8. glaher is described as smooth. The species 

 definitely included in this genus are : — 



Pentremites melo, Owcxi and Shumard. Subcarboniferous, 

 Iowa, Missouri, Illinois, &c. 



P. 8ayi, Sliumard. Ditto. 



Grancttocrinus melonoides. Meek & Worthen. Burling- 

 ton group (Subcarboniferous), Iowa. 



G.j^i^um, Meek & Worthen. Burlington group, Iowa. 



G. neglectus, Meek & AVorthen. Ditto. 



G. glaber, Meek & Worthen. St. -Louis group, Illinois. 



