80 paljBontolooy op new-york. , • 



This species, allliough 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, (hough it never occurs so abundant- 

 ly as other species do in the slates above. 



Fig. 1 1 a. A group of these fossils ; all the stipes, except one, having been broken off by a fracture of 



the stone. 

 Fig. 1 1 A. 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. 

 Plates XXVIL, XXVIH. & XXIX. 



Nolwitlistanding the fact that some portions of the Trenton limestone are composed in a 

 great degree of the broken and comminuted remains of the Crinoidea, still it is very rare 

 to meet with specimens approaching to perfection. Much diflSculty 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 Crinoidea of this ancient period, we have, in the Family Echino- 

 DERMATA, the Gcuus AsTERiAs, whicli appears in this rock in unequivocal form and 

 condition.* 



The Crinoidea 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 Abterias 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. 



