NIAGARA GROUP. 
195 
Genus ICHTHYOCRINUS (Conrad). 
This genus is characterized by Mr. Conrad (Jour. Acad. Nat. Sci. Philadelphia, Yol. viii, p. 
279), as follows: 
“ Column round, smooth • canal small and round ; scapulae with the margins of the articu- 
tions parallel, and somewhat imbricated.” 
These characters are not sufficiently decisive, and alone do not enable one to distinguish the 
fossil. 
The column is round, smooth and slender, having the articulating rays on the outer circum¬ 
ference. The base of the cup shows five small triangular pelvic plates, succeeded by scapular 
plates resting on the oblique upper edges of the pelvic plates : a second and third scapular 
plate succeed in direct series, when subdivision takes place, which is repeated two or three 
times at irregular intervals. The base of the cup, when the column is separated, presents a 
tripetalous impression, which is probably of generic importance. 
This genus is known only in a single species ; but it possesses peculiarities of high interest, 
showing its relations to crinoids with three pelvic plates ; while the arms proceeding in direct 
line from the second series of plates, is characteristic of the lower forms with pentapetalous 
calyx. 
588. 1. ICHTHYOCRINUS L.UVIS. 
Pl. XLIII. Fig. 2 a-p. 
Ichthyocrinus lavis. Conrad, Jour. Acad. Nat. Science, Vol. viii, pag. 279, pl. 15, fig. 16 
Column slender, round and smooth, gradually enlarging towards the base of the cup, and 
composed of alternating thicker and thinner joints ; base of the cup showing a tripetalous 
impression (or three undeveloped pelvic plates surrounding the centre) ; pelvic plates five, 
triangular, with wide bases ; on one side an interval between the pelvic plates, allowing one of 
the second series to rest upon the column (see figs. 2 f , g) for a narrow space ; second series 
having the form and position of scapular plates ; lower side resting on the sloping sides of the 
pelvic plates ; upper edge nearly parallel to the lower, giving the succeeding plates the same 
form on the lower side, each series alternating with that laterally in juxtaposition ; first sub¬ 
divisions taking place in the fourth or fifth plate from the pelvis ; second subdivisions occurring 
on the sixth or ninth plate from the first one, and beyond this at irregular intervals ; plates 
obtusely angulated on the exterior surface from the centre of the base to the sinus on the upper 
edge, articulated on their upper and lower surface by marginal crenulations. On the side where 
the plate of the second series rests on the column, there are two supernumerary plates inter¬ 
calated on the lefthand side and above its upper lefthand angle. The subdivisions, though 
apparently commencing by the division of a single plate, still show one edge elevated a little 
higher than the other, so that the series are in their lateral relations alternate with one another, 
