1«6 PALJIONTOLOGY OF NEW-YORK. 



In 1848 the late Edward Forbes published, in the Memoirs of the Geological 

 Surrey of Great Britain, Vol. ii, Part ii, au article "On the Cystidete of the Silurian 

 Rocks of the British Islands," in which he redcscribed the Genus Pseudocrinites of 

 Pearce, and proposed for another one of similar structure the name ^piocystites. 

 The essential structure of the body does not difler in these two genera; and it was 

 mainly upon the mode of lodgment of the arms in the grooves upon the surface of 

 the body, and the peculiar mode of articulation of the ossicula, that the distinction 

 was founded. 



I have identified a species of the Genus Jlpiocystites in the Niagara group, which 

 Is published in Vol. ii. Palaeontology of New- York ; remarking at the same time 

 upon the close agreement in character between Lepadocrinus of Conrad, and Pseudo- 

 crinites as described and illustrated by Mr. Forbes. 



In the Genera Lepadocrinus, Jlpiocystites and CaJlocystites, the structure and ar- 

 rangement of the arms and fingers are so similar, that upon the characters presented 

 by these alone, no generic distinction could be made. It does not appear to me to 

 be fully shown that these appendages in Pseudocrinus are so diflerent from those of 

 ^piocystites, as to warrant the establishment of a distinct genus ; and regarding 

 fundamental structure as the more important character, I would feel disposed, from 

 the knowledge at present possessed, to include Lepadocrinus, Pseudocrinus and Apio- 

 cystites under one generic term. 



Although the description of Mr. Conrad, published in 1840, was too incomplete 

 to enable one to recognize the fossil, yet the figure given in Mr. Mather's Report 

 in 1843 was quite sufficient to attract attention; and I can only suppose that this 

 volume had escaped the notice of Mr. Forbes, or he would have made some com- 

 parisons of this genus and species with the British cystidians described by him in 

 1845. 



Following Mr. Forbes in my second volume of the Palaeontology of New- York 

 I adopted the name Jlpiocystites for a species in the Niagara group; supjxising at 

 the same time, with the specimens which were then before me, that I should find 

 sufficient distinctions between that fossil and the one under consideration, to sustain 

 the Genus Lepadocrinus also. After careful comparison of all the specimens in my 

 possession, I am unable to observe any generic distinctions between the Niagara and 

 the Lower Helderberg forms. I shall, however, continue the use of the name Lepa- 

 docrinus, since it has precedence in point of time, and is now pretty well known 

 among geologists of the United Strtes. 



Tlie structural differences between the Lepadocrinus of the Lower Helderberg and 

 the Jlpiocystites of the Niagara are not greater than occur in many species of crinoids 

 of the same genus, where various modifications take place in the plates of the upper 

 part of the body; and even in two specimens of the same species oi Jlpiocystites in 

 the Niagara group, there are differences quite as great in the arrangement of the 

 upper plates, as between that species and the one now under consideration. 



