80 PALEONTOLOGY OF NEW-YORK. 
This species, although compressed, has still considerable thickness of substance, unlike 
those in the slate, which are compressed to extreme tenuity. The substance appears to 
have been partially calcareous, or at least corticiferous, and, being imbedded in compact 
limestone, has retained more nearly its original character than those imbedded in the soft 
shales, where any calcareous matter would have been removed. The central stipe is clearly 
surrounded by small triangular scales, which sheath at the base, and taper abruptly to an 
acute point above. This structure, where the whole is flattened, gives a serrated character 
to the stipes. 
This fossil is not uncommon in the Trenton limestone, though it never occurs so abundant- 
ly as other species do in the slates above. 
Fig. 11 a. A group of these fossils; all the stipes, except one, having been broken off by a fracture of 
the stone. 
Fig. 11 6. An enlarged portion, showing the edges of the sheathing scales. 
Position and locality. In the central part of the Trenton limestone. Trenton Falls, Mid- 
dleville, &c. 
CRINOIDEA OF THE TRENTON LIMESTONE. 
Pirates XXVIIL, XXVIII. & XXIX. 
Notwithstanding the fact that some portions of the Trenton limestone are composed in a 
great degree of the broken and comminuted remains of the Crinorea, still it is very rare 
to meet with specimens approaching to perfection. Much difficulty has been encountered 
in consequence of this circumstance, since the numerous fragments of columns, apparently 
belonging to different species, rendered it necessary to make some disposition of them. 
One or two fortunate discoveries, among this family of fossils, has enabled me to decide 
satisfactorily as to the reference of the columns which are most numerous, leaving but few 
undetermined fragments. 
In addition to the Crinorea of this ancient period, we have, in the Family Ecurno- 
DERMATA, the Genus AstTEeRras, which appears in this rock in unequivocal form and 
condition.* 
The Crrnorea of this period are not only specifically distinct from those in the succeeding 
geological eras, but, together with those of the Hudson-river rocks, present the characters 
of a group or family quite distinct from any similar group in the higher strata. 
* The small tubercle, from the Chazy limestone, figured on Plate iv., though perhaps not entirely satisfactory as 
proof of the existence of Asrrrias at that period, offers a presumption which is strengthened by the occurrence of 
an unequivocal species in the Trenton limestone, several individuals of which have been found. 
