OKM:I; I 



BLASTOIDKA 



195 



very narrow. extending to the base. Spim- !-. M -i rule, distinctly double, 

 but sometimes incompletely divided. Lancet-plate perfectly, or for the most 



part, concealed by >ide plates. Carboniferous; Belgium, England, North 

 America. .]/. .-//// /*////*, Koeiner. 



Family ~2. Troostoblastidae. Etheridge and Carpenter. 



Ambulacra narrow, linear, deeply impressed, descending outward from the summit. 

 confined to the narrow upper end, invisible externally, except the posterior one 

 in '/'/'" -.-/",/ //n/.s-. Ln ncet- plate entirely concealed by side-plates. A 



f, rqprtttntod !/ lineal slits at the sides of the deltoid 

 ', a nil IK it l><> a mled by side-plates. Silurian to Sub-Carbon- 

 iferous (Warsaw Group). 



Troostocrww, Shum. (Fig. 321). Calyx narrow, elongate, 

 somewhat fusiform, with contracted, subtruncate, or slightly 

 convex upper face. Ambulacra short. The four anterior 

 deltoids overlapped by the radia limbs; the posterior one 

 much larger than the rest, and appearing externally. Posterior 

 spiracles confluent with the anus. Silurian (Niagara Group) ; 

 North America. 



Metablaslus, E. and C. Like the preceding, but all the 

 deltoids equal, and the two posterior spiracles not confluent 

 with the anus. Spiracle slits ten in number; hydrospires 

 four lo each side of an ambulacrum. Silurian to Sub-Car- , 



. ... 1 roostocnnus Rein- 



boniferous. iw ,-,/, Troost sp. 



Tricoelocrinus, M. and \V. Calyx pyramidal, broadest below faffe" ; RoeTner"'. 

 and narrowing upwards; when seen from above or below, da? al '(naf rom 8 izex 

 strongly pentagonal in outline, owing to the projecting and Lf^, 1 ' 1 asl " (t 

 carinated character of the radials. Deltoids small ; ambulacra 



long, and extremely narrow. Spiracles ten, dis- 

 tinct ; anus large. Hydrospires small, enclosed 

 within the substance of the forked plates. Sub- 

 Carboniferous. 



Family :i. 



Nucleoblastidae. 

 Carpenter. 



Etheridge and 



Fie. 



Elaeacrinus * Verneuili, Troost sp. 

 Lower Devonian ; Columbus, O. (after 

 II'M-mcr). .1. SHIe-VteW of calyx. 

 /-', H;is,-. C, Ventral surface. I), Same, 

 enlarged. 



Calyx usually globular or ovoidal, with flattt m><l 

 or concave base, and linear ambulacra extending the 

 //7/r<V length of the calyx. Spiracles distinctly double, 

 and chiefly formed by the apposition of notches in the 

 1 <i if' ' -plate and deltoids. Devonian and Sub- 

 Carboniferous. 



Etheridge and 



Sub-Family A. ELAEACRINIDAE. 

 Carpenter. 



Posterior deltoid divided into two parts by an anal 

 plate. Anus distinct from the posterior spiracles. 



Elaeacrinus, Roemer (Nucleocrinus, Conrad), (Fig. 322). Basals small, 

 inconspicuous, sometimes hidden within the columnar cavity. Radials small, 



