CLASS II 



BLASTOIDEA 



169 



Onjptoschisvia E. and C. Calyx elongated, with a broad, .flat, truncated 

 upper face. Radial sinuses wide and open, their sloping sides pierced by 

 hydrospire slits, which are completely concealed by broad, petaloid ambulacra. 

 Spiracles small, single or more rarely double ; in the latter case the posterior 

 pair are confluent with the anus. Rej^resented by the solitary species C. 

 schuUzi d'Archiac and de Vern. Lower Devonian ; Spain. 



Ofopliocrinus v. Seebach (Dimorphocrinus d'Orb. ; Codonitcs M. and W.), 

 (Figs. 258 D, 261). Calyx balloon-shaped to truncate ob-pyramidal, with 

 more or less concave upper face. Section distinctly pentagonal or stellate. 

 Ambulacra narrow, linear to sub-petaloid. Deltoids generally visible in side- 

 view, the posterior one wider than the others. Spiracles ten, varying from 

 wide clefts along the sides of the ambulacra to narrow slits at their upper 

 ends ; the posterior pair separate from the anus. Hydrospire-slits almost 

 completely concealed, being concentrated at the bottom of the radial sinuses. 

 Stem round, composed of short, nearly equal joints. Pinnules extending to 

 nearly twice the height of the calyx, of uniform thickness throughout, and 

 composed of sharply cuneate pieces interlocking from opposite sides ; ventral 

 furrow wide, and covered by small pieces. Lower Carboniferous ; Britain, 

 Belgium and North America (Kinderhook and Burlington Groups). 



Family 2. Pentremitidae d'Orbigny. 



Base usually convex', and often much elongated. Spiracles five, but sometimes more 

 or less completely divided by a median septum, and bounded proximally by the upper- 

 most side-plates. Lancet-plate either entirely visible or partially covered by side-plates 

 which extend to the margins of the ambulacra. 

 Hydrospires concentrated at the lowest part of the 

 radial sinus. Devonian and Lower Carbon- 

 iferous. 



Fentremites Say (Figs. 254-7, 262-3). 

 Calyx usually ovate or pyriform, with elon- 

 gate, sub-truncate base. Ambulacra broad, 

 sub-petaloid. Lancet-plate wholly exposed, 

 and resting below on an under lancet-plate. 

 Side-plates and outer side-plates numerous, 

 the former abutting against the edges of the 

 lancet-plates. Hydrospires three to nine ; 

 spiracles single, or occasionally double ; the 

 two of the posterior side confluent with the 

 anus, and forming with it a single large 

 orifice. Oral centre surmounted by numerous 

 spines, placed closely against one another so 

 as to form a pyramid, which comjoletely covers 



the summit and the greater portion of the Lower carbon- Roemer. Lower Carbon- 

 1 Ti . , '', 1 , • ,1 T iferotis ; 111. iferous ; 111.; A, Summit 



spiracles, liixcessively aoundant in the Lower (Nat. size). aspect, b, base. 



Carboniferous of North America (Burlington 



to St. Louis and Kaskaskia Groups), but not identified in Europe. P. godoni 

 Defrance, and P. pyriformis Say, are the most familiar species. 



Pentremitidea d'Orb. Calyx clavate-pyramidal, with elongate, usually 

 conical base, and truncate or convex ujjper face. Ambulacra narrow, short ; 



Fig. 202. 



Fentremites 

 qodoni Defr. 



Fio. 263. 

 Fentremites siilratus 



