178 
PALAEONTOLOGY OF NEW-YORK. 
form, though connected with a great variety of structure in the upper part of the calyx. The 
first deviation from this structure in the true crinoids, appears in a tripetalous impression on the 
base of the calyx, and a canal of the same form in the column. Thence proceeds the tripetalous 
base or pelvis, which characterizes a small group of these fossils mostly of very simple structure 
and few appendages. 
In the Genus Hypanthocrinus, we first perceive a remarkable deviation from the true 
crinoid type. The arms, which are usually expanded or expansible, are contracted, and with the 
tentacula or other appendages folded closely together ; each pair being separated by a solid 
vertical plate reaching nearly to the centre, and converging, as do the enfolded arms, towards 
the apex, which is surmounted by a few small plates forming a kind of proboscis over the 
cavity of the stomach. This appears to be the first type developed in the direction of the 
Pentremites; the pairs of arms representing the ambulacral areas, while the solid plates repre¬ 
sent the interambulacral spaces. In fact the Hypanthocrinus appears to be nothing more than a 
monstrous Pentremite. 
In another direction, and still bearing some analogy with Pentremites and also perhaps 
more with the Genus Eugeniacrinites, we have the Stephanocrinus, presenting peculiarities 
not observed in any species of this class of animals from the succeeding strata. 
The Caryocrinus, which is regarded by Yon Buch as forming the passage from the true 
Crinoidea to Cystidea, is the most abundant species of the group, and is one of the most 
interesting forms. The true Cystidea, of which a single species was noticed in the Trenton 
limestone, appears in several beautiful forms at this period. 
It was not until within the past two or three years that these fossils were added to the list 
of our species, by the persevering researches of Col. E. Jewett of Lockport, who has not 
only contributed these beautiful forms to our knowledge, but has by his collections increased 
the number of species among the Crinoidea previously known to us, by one third of all the 
species here given. 
Notwithstanding the great variety of forms among animals of this class, at this period, there 
appear to be no true Carboniferous or Devonian types. The genera Platycrinus and Actino- 
crinus are not represented, and the species sometimes thus referred have not the-true structure 
of these genera. 
