M'.sriv'H'TloNN OF T1IF> SI'1-.CIKS. 191 



A. Base long and tapering, 



1. Posterior spiracles confluent with | 



anus. The anal deltoid visible > Troostocrinus, Shumard. 



externally. J 



2. Posterior spiracles separate from 



anus. Deltoids all alike. 



■ MetablastU3, H. & C. 



B. Base small, more or less truncated, and") 



hollowed at the sides of the trihedral facet. I Triccehcrinus, Meek & Worthen. 



Deltoids all alike. No anal spiracle. I 



Genus TROOSTOCRINUS, F. II. Shumard, L865 (emend. E. & C, 1886). 

 Pentatrematites Clavati, Rocmer, Archiv f. Naturgcsch. 1851, Jahrg. xvii. Bd. i. p. 372. 

 Troosticrinus, Shumard (pars), Trans. St. Louis Acad. Sci. 18G3, vol. ii. no. 2, p. 381- (note). 

 Troostocrinus, Meek & Worthen (pars), Proe. Acad. Nat. Sci. Philad. 1868, p. 356. 

 Troostocrinus, Meek & Worthen (pars), Report Geol. Survey Illinois, 1873, vol. v. p. 507 



(non White). 

 Troostocrinus, E. & C. (pars), Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 247. 



Gen. Char. Calyx narrow, elongated, and somewhat fusiform ; summit contracted, 

 subtruncate, or slightly convex; base elongate and tapering, rounded above, but 

 triangular below ; section pentagonal ; periphery nearly one third of the height 

 from the summit. Basal plates about one third as high as the calyx. Radial plates 

 long and narrow, the limbs much shorter than the bodies, and inclined to them at a 

 very open angle ; sinuses short, narrow, and almost parallel-sided. The four anterior 

 deltoid plates overlapped by the radial limbs and confined to the summit ; the posterior 

 one larger, and appearing externally above the radial limbs as an unequally rhombic 

 plate. Ambulacra short, and somewhat deeply set in the sinuses, especially at their 

 proximal ends. Ten to twenty side plates, entirely concealing the lancet-plate. Fixe 

 small spiracles, the four anterior ones more or less completely divided by the deltoid 

 ridge, and the posterior one confluent with the anus. Hydrospires pendent, with 

 three folds on each side. 



History. This genus was proposed by Dr. F. B. Shumard l , in his useful " Catalogue 

 of North-American Palaeozoic Fossils," pt. 1 2 , for subfusiform species of Pcntremites, 

 after the type of P. Reinwardti, Troost, possessing a slender outline, triangular base, 

 and linear ambulacra. The genus was never described in detail, but was adopted 

 provisionally in 18G8 by Messrs. Meek and Worthen 3 . 



Dr. Shumard's remarks referred to above are as follows : — " There appear to me 



1 We write Troostocrinus on the principle of plurimorum auctoruw ; but the name was spelt Troosticrinua 

 by Shumard. 



a Trans. St. Louis Acad. Sci. 1865, vol. ii. no. L', p. :; x I. 

 a Proc. Acad. Xat. Sci. Philadd. 1868, p. :;."»t;. 



