188 
PALEONTOLOGY OF NEW-YORK. 
Genus THYSAN O'C RIN U S ( nov. gen.). 
[ Gr. &v<fa.voi, fimbria , and xpwov, lilium; from the fimbriated arms or fingers of the species included 
under this genus.] 
Column round; pelvis composed of five pentagonal plates; costal plates five, hexa¬ 
gonal ; scapular plates alternating with the costal plates, bearing a second scapular plate, 
and an arm-joint on which the subdivisions of the arms take place; a single interscapu¬ 
lar and two second interscapulars; arm divisions composed of a single series of plates in 
the lower part, and a double alternating series in the upper part. Or, the arm-joint suc¬ 
ceeded by a hand of one or more joints in direct succession, succeeded by fingers com¬ 
posed of a double alternating series of joints. 
The essential characters here presented, it is believed, will be found in a number of 
species, all having the arms composed, particularly in the upper portions, of a double 
series of joints with jointed tentacula. The interscapular plates will probably not be 
found constant in all species, but they are clearly present as described in the specimen 
fig. 1 a, pi. 42, and also in fig. 4 & of the same plate. The fragments of arms of other 
species with tentacula having similar characters, show the group to be a natural one, and 
containing several species. 
582. 1. THYSANOCRINUS ULIIFORMJS (n. sp.). 
Pi. XLII. Fig. 1 a -/. 
Body cup-form, subangular; surface of plates ornamented by vertical or radiating, 
interrupted or crenulated, sharp, elevated striae; pelvic plates small; costals larger, and 
succeeded by five still larger scapular plates, from which in direct series originate the 
arms and fingers; arm-joints succeeded by three simple hand-joints; fingers composed 
of a double series of joints, fimbriated ; column round, composed of alternating thicker 
and thinner joints, which are more irregular near the base of the cup. 
The surface ornament of this species is quite peculiar and distinctive : on the plates 
near the base it is radiating, and sonfetimes granular; on the higher plates, interrupted, 
nearly vertical strife; and on the plates of the fingers the strife extend quite across the 
plate somewhat obliquely, and are sometimes granulated. The structure and arrangement 
of the plates, to the commencement of the arms, are only of generic importance, though 
the forms are slightly different from another species. The joints of the fingers are wide, 
and the tentacula are quite distinctive when compared with others, as showm on the 
same plate. The first joint is narrow and long, very gradually tapering; the succeeding 
joints are somewhat longer than the first, distinctly angular, with the angles crenulate 
or asperate. 
Where the fingers are crushed, and one side only shown, they appear to be composed 
of a single series of plates only, since the line of joining of the two rows of the plates 
on the back is so nearly vertical. 
