DESCEDPTIONS 01 I'm: SPECIES. 195 



>'y. Char, Calyx elongately fusiform ; summit subtruncate, and much contracted, 

 the rapid attenuation of the calyx above the periphery Lining to it an almost pointed 

 appearance; base long and slender; interbasal sutures straight, and not well defined; 

 section pentagonal, the sides straight above the radial lips, but below them Bomewhat 

 concave; periphery rather more than one fourth the total length of the calyx from 

 the summit. Basal plates forming a slender cup, rounded above, but triangular 

 below, with flat sides, and slightly constricted at its lower end. Radial plates very 

 narrow and lon^ ; bodies one and a quarter times as long as the limbs, and Bubangular 

 in the middle line; limbs with flat sides; interradial sutures lodged in very faint 

 depressions; sinuses short, very narrow, almost parallel-sided, with sharp margins; 

 lips simple, not produced. Normal deltoid plates invisible externally, and little 

 more than sharp crests beneath the radial limbs ; the azygos one unequally rhombic, 

 with its crest truncated by the anus. Ambulacra short and narrow, rather below the 

 edges of the sinuses; side plates and outer side plates alternately triangular, from 

 twelve to thirty in number, and entirely concealing the lancet-plates. Spiracles 

 almost completely divided into linear slits by the deltoid crests ; the posterior one 

 confluent with the anus. Three hydrospire-folds on each side of an ambulacrum. 

 Column unknown. Ornament of closely set, microscopically fine lines parallel to the 

 margins of the plates. 



Remarks. This species is readily distinguished from the only other one which we can 

 refer to Troostocrinus by its divided spiracles and by the sharp angle in the calyx at 

 the leA'el of the radial lips. Troostocrinusl Grosvenori, as figured by Shumard 1 , has 

 wider ambulacra, undivided spiracles, and a calyx which tapers regularly, but slowly, 

 downwards from a line considerably above that of the radial lips. 



Metablastus lineatus resembles T. Seinwardti in the doubly conical shape of the 

 calyx, but the ambulacra are relatively much longer, and there are ten spiracles in 

 addition to the anal opening (PL III. figs. 14. 15). There are various other more or 

 less fusiform species of so-called Pentremites which may, perhaps, have to be referred 

 to Troostocrinus when the characters of their summit are properly known. Such, 

 for example, are P. bipyramidalis, Hall, and P. Wbrtheni, Hall, both from the 

 Keokuk Group of America, and P. Varsouviensis, Worthen, from the Warsaw Lime- 

 stone of Illinois ; but we are inclined to think, as we shall explain subsequently, that 

 they belong to Metablastus. The Troostocrinus Wachsmuthi of Gurley 2 certainly 

 belongs to this genus, as the anus is distinct from the spiracles at its sides. But 

 we are in some doubt about the type from the Lower Devonian of Spain, which 

 we formerly described as Troostocrinus J/isjianicus 3 (PL V. fig. 21), as its summit is 

 not sufficiently well preserved to show the generic characters properly. But it is a 



1 Tr;ui>. s t . Louis Acad. Sci. 1858, vol. i. no. 2, pi. '■'. fig. 2d. 

 - 'New Carboniferous Fossils.' Bulk-tin no. :.'. Feb. 25, L884, p. 1. 

 ■ Ann. & Mag. Nat. Hist. 1SS3, vol. xi. p. 245. 



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