206 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



allied Si/mhathocrinus, Allagecrinus and Hajjlocrmus, the ventral disk consisted 

 of orals only, and the plate fitted approximately upon the cup of one of the 

 species, which occurs in the same bed. A well preserved oral pyramid of this 

 genus is figured on Plate III. Fig. 15, which may belong to this species. 



(?) Idiocrinus immaturus (Hall). 

 Plate XVIII, Figs. 10a, h, c. 



1851. Thysanocrinus immaturus — ^ Hall; Palseont. N. York, Vol. II., p. 191, Plate 49, Figs. ^a-f. 



This small species, so far as known, in its general habitus so closely 

 resembles Idiocrinus that we are inclined to regard it as belonging to this 

 genus. It is more depressed than L elongatus, the sides of the cup are more 

 convex, the base more concave, and the costals proportionally higher. 

 Neither arms nor ventral disk are known. 



Horizon and Locality, — Niagara group ; Lockport, N. Y. 



(?) Idiocrinus tennesseensis (Worthen). 

 Plate XVIII, Fig. 11. 



1890. Centrocrinus tennesseensis — Worthei^^ Geol. Rep. Illinois, Vol. VIII., p. 95, Plate 14, Fig. 1. 



Dorsal cup apparently obconical. Plates almost flat, and without orna- 

 mentation ; suture lines indistinctly grooved. 



Infrabasals three, forming a slightly projecting rim around the bottom of 

 the calyx. Basals rather large, fully as high as wide, three of them pentan- 

 gular, the others being covered by matrix. Eadials one fourth wider than 

 long, the lower faces distinctly angular. Costals two, narrower than the 

 radials ; the first quadrangular and extremely short, more than three times 

 as wide as long ; the second a little longer than the first, and obtusely an- 

 gular above. Disticlials two in the calyx ; the proximal one as long as, or 

 longer than, the axillary costal ; the second a little wider than the free arm 

 plates, but not higher. Arms two from the calyx, moderately stout; com- 

 posed of rather long, quadrangular joints, branching (at least in one of the 

 arms) from the fourth free plate. Interbrachials, as seen at two sides, subel- 

 liptical, extending to the full height of the first distichals, slightly grooved 

 longitudinally at the median line. Stem round, the nodal joints high, the 

 outer faces convex and somewhat projecting. All other parts of the species 

 unknown. 



