DESCRIPTIONS OF THE si'l'i lis. I'll 



sometimes approaching to decagonal, with straight sides. Basal plates small and 

 inconspicuous, invisible in a side view, and hidden within the columnar cavity. 

 Radial plates small, forming a low expanded cup or basin ; limbs short, with the 

 proximal margins scalloped; bodies greatly reduced in size, distal Is reflected within 

 the columnar pit; lips prominent, constituting a quinquepod on which the calyx 

 rests. Deltoid plates greatly enlarged and elongated, usually lanceolate, forming 

 quite or more than two thirds of the entire calyx; anal interradius wider than the 

 others, more prominent, giving to the body a slightly unsymmetrical outline, its 

 deltoid being divided into two parts by an anal plate ; each of the other deltoids is 

 superficially divided into three parts by two more or less distinctly impressed lines 

 parallel to the margins of the plate. Radio-deltoid sinuses narrow, extending the 

 whole length of the calyx from the summit to the base, the radial portions very short 

 and shallow. Ambulacra similar in size and length, sometimes prominent, almost 

 entirely enclosed by the deltoid plates; lancet-plates exceedingly long and very 

 narrow, but entirely tilling the radio-deltoid sinuses, and partially exposed ; side 

 plates and outer side plates numerous, sometimes almost ninety in number. Hydro- 

 spires pendent, two tubes on each side of an ambulacrum ; spiracles ten in number, 

 arranged in five pairs, which notch the proximal ends of the deltoid plates. Mouth 

 large when exposed, but normally closed by five or more summit plates which form a 

 flattened dome above the peristome. Anus more or less horizontal in position, 

 closed by one or more plates, and distinct from the posterior spiracles, which are 

 somewhat smaller than their fellows. Column round or imperfectly pentagonal. 

 Ornament " striato-cancellate, or striato-granulose." 



History. The generic value of this type was first noticed by Conrad l , who gave an 

 imperfect description of it in 1842 under the name of Nucleocrmus. His description, 

 which was accompanied by a figure of his type species N. elegans, runs thus : — " This 

 genus differs from Fentreni'dcs, Say, in having only one perforation at the top, which 

 is central." 



In 1849 Dr. G. Troost 2 gave a list of fossil Crinoids found in Tennessee. 

 Amongst these occurs the name Olivanites Yertieuili, but it is unaccompanied by 

 any generic description. In the year 1851, however, Dr. F. Roemer 3 published an 

 elaborate account of this fossil, and showed that it represented a new generic type, 

 for which he proposed the name of Elceacrinus. A few years later, however, Lyon 4 

 came to the conclusion that Roemer's material had not been sufficiently well pre- 

 served, and that in consequence of this " both the figures and description are 

 defective in many respects. For these reasons, and possessing quite perfect specimens, 



1 Journ. Acad. Nat. Sci. Philad. 1842, vol. viii. pfc. 2, p. 280, pi. xv. fig. 17. 



2 Americas Journ. Sei. 1849, vol. viii. p. 419, 



3 Archiv f. Xaturgesch. 1851, Jahrg. xviii. Bd. 1, p. 375. 



4 Palifioutological Report, Owen's 3rd Report Geol. Survey Kentucky, 1857, p. 487. 



2k 2 



