178 PALJEONTOLOGY OF NEW-YORK. 



I'orm, though connected with a great variety of structure in the upper part of the cal}'x. The 

 tirst 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 tlie column. Thence proceeds the tripetalous 

 base or pehns, 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 w^ith 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 arens, 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 Von Buch as forming the passage from the true 

 Oinoidea 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 Platycrints and Actino- 

 cRiNvs are not represented, and the species sometimes thus referred have not the true structure 

 of these genera. 



