194 CATALOGUE OF THE BLASTOIDEA. 



As a general rule, the sharp median ridges of these deltoid plates almost completely 

 separate the proximal ends of the narrow radial sinuses at their sides, which remain 

 open as the linear spiracles; but in T. Grosvenori this does not appear to be the case, 

 and there are only five spiracular openings. This species thus differs from T. Eein- 

 wardti in the same way as our two specimens of Pentremites elongatus figured on 

 PI. I. figs. 4, 5, differ from one another; while in Pentr emit idea angulata (PL IV. 

 fig. 14) two of the spiracles are completely divided, and a third not. It is to this 

 latter genus that Troostocrinus seems most closely allied. Each has a long basal 

 cup, narrow ambulacra, and an undivided anal spiracle ; while both species of 

 Troostocrinus approach P. Paillettei and P. Lusitaniva in outline (PI. IV. figs. 9, 

 11; PL V. fig. 20; PL XII. fig. 11 ; PL XIV. fig. 13). These two, however, are 

 rather extreme forms of the genus, which is very closely linked with Pentremites, 

 especially in the structure of the spiracles. The side plates project beyond the 

 lancet-plate so as to bridge over the hydrospire-cleft, and convert it into a canal, as 

 seen in PL IV. fig. 14, and PL V. fig. 19; while in Troostocrinus the spiracle is the 

 open proximal end of the hydrospire-cleft, which is closed distally by the ambulacrum 

 slightly increasing in width and meeting the sides of the radial sinus as in Metablastus, 

 Schizoblastus, and Ekeacrinus (PI. HI. figs. 3, 14 ; PL XVI. tig. 12; PL XVIII. 

 fig. 10). 



Distribution. The type species, Troostocrinus Reinwardti, is characteristic of the 

 Niagara (or Wenlock) Period in the Upper Silurian of America. No Devonian 

 species are known, but if, as we suspect, Pentremites Grosvenori, Shumard, be 

 referable to this genus, it reappeared in the upper strata of the American Carbo- 

 niferous Limestone. 



Type. Pentremites Peinwardtii, Troost. 



Troostocrixus Reinwardti, Troost, sp. 



(Fig. VII.; PL XII. figs. 11, 12; PL XVII. fig. 17.) 



Pentremites Reinwardtii, Troost, Trans. Geol. Soc. Pcnnsylv. 1835, vol. i. p. 224, 1. 10. ft'. 10, 1 1 . 

 "Pentremites Reinwardtii, Troost, Fifth & Sixth Geol. Reports, State of Tennessee, 1840 and 



1841, pp. 58 & 14. 

 Pentremites Reinwardti, Yandell & Shumard, Coatrib. Geol. Kentucky, 1847, p. 0. 

 Pentremites Reinwardti, Roemer, Neues Jahrb. f. Mineral. 1848, p. 296. 

 Pentremites Reinwardtii, Yandell, Proc. American Assoc. Adv. Sci. for 1851 [1851], p. 232. 

 Pentatrematites Reinwardtii, Roemer, Arehiv f. Naturgcsch. 1851, Jahrg. xvii. Bd. i. p. 372, 



t. 0. f. 12 «-e. 

 Pentatrematitet Reinwardtii, Roemer, Sil. Fauna W. Tennessee, 1860, p. 00, t. 3. f. 2 a-c. 

 Pentatremites Reinwardti, Broun, Classen and Ordn. Thier-Reichs, 1800, Bd.ii.t. 23.f. 4 a, b. 

 Pentremites Reinwardtii, Dajardin & Hupe, Hist. Nat. Zooph. Echinod. 1802, p. 99. 

 Troosticrinus Reinwardtii, Shumard, Trans. St. Louis Acad. Sci. L865, vol. ii. no. 2, pp. 384, 



385 (note). 

 Troostocrinus Reinwardtii, L. & ('., Ann. 6^ Mag. Nat. Hist. 1882, vol. ix. p. 249. 



