Geology. 



121 



most important peculiarities, and we regarded it as being merely a species 

 of Pentremites (Say), analogous to (P. Elceacrinus) Verneuili (Rcemer). 

 Afterwards, through the politeness of S. A. Casseday, Esq., of Louis- 

 ville, we were put in possession of two individuals in a more perfect state 

 of preservation, and these, with some specimens since found by ourselves, 

 have furnished the material from which we are enabled to add a new and 

 interesting genus to the family Blastoidea. 



Eleutherocrinus, Nov. Gen. — Agreeable to the plan pursued by 

 Messrs. de Koninck and Le Hon, we give as the formula of the genus — 



Basal pieces, 3. — One small, two irregular and very much elongated. 



Radial pieces, 1X5. — Four-forked, occupying nearly the whole length, 

 one short and not forked. — Inter radial pieces, 1X5. — Small. 



Pseudoambulacral areas, 5. — Four linear extending nearly the entire 

 length of the calyx, one short, sub-triangular, situated on the summit 

 plane. — Column, none. — Ovarial apertures, 8 (?) 



Generic characters. — The calyx is of an elliptical form, truncated at 

 summit and subtri angular at base. 



Base very irregular in form, sub-triangular at its lower part, and 

 prolonged on one of its sides to a remarkable length. It consists of 

 three pieces, one of which is small, lozenge-shaped ; the other two are 

 precisely alike, very large and prolonged nearly to the middle of the 

 calyx. These latter pieces are joined together in the median line by a 

 straight suture, with which their external edges are sub- parallel, except 

 the inferior fifth, which exhibits a small angular fold, directed obliquely 

 forwards to articulate with the inferior edges of the single basal piece. 

 The superior edge of this fold is also emarginated to receive the extremity 

 of an elongated radial piece. 



Radial pieces: four are non-symmetrical, occupy nearly the entire 

 length of the calyx, and are channelled almost to the base for the recep- 

 tion of the pseudoambulacrae. The middle pair alternate with the single 

 basal, the exterior ones repose on the emarginated edges of the fold of 

 the large basals. The fifth radial piece scarcely exceeds one-half the 

 length of the others, though it is much wider. It rests on the upper 

 edges of the large basals and between the superior half of two of the 

 long radials. Its upper edge reaches to the level of the summit plane. 

 The surface is destitute of a pseudo-ambulacral groove. 



Interradial pieces : five, small, alternating with the radials. Three of 

 them are somewhat lozenge-shaped ; two irregular in form, articulate 

 with the short radial piece. 



Pseudoambulacral areas : four are linear, commence at the central sum- 

 mit, opening and descend nearly to the base ; the fifth is triangular and 

 lies horizontally on the summit plane just within the edge of the short 

 radial piece. 



Ovarial apertures : only eight of these openings are visible in the 

 specimens under examination ; two are situated at the extremity of each 

 lozenge-shaped interradial, each pair being divided by a mesial septum ; 

 but at the extremity of each irregular interradial there is apparently 

 merely a simple round opening without any visible septum. No anal 

 opening is to be seen in our specimens. Mouth nearly central. 



SECOND SERIES, VOL. XXII, NO. 64. — JULY, 1856. 16 



