IS© 
PALAEONTOLOGY OF NEW-YORK. 
This genus is constituted to receive some very peculiar crinoidal remains, which, 
till within a short period, were not fully understood. In the arrangement and en¬ 
graving of Plate v in 1855, the figures 8 to 12 inclusive express all that was then 
known regarding these fossils ; which had been observed as hemispheric or sub- 
conical bodies with entirely smooth surfaces, giving no evidence of the point of 
attachment for a column, and having the margins adhering to the imbedding stone, 
or the cavity filled. On carefully freeing several of these from the stone, the forms 
and character presented in the figures became apparent. In fig. 12, the cavity ap¬ 
pears as if closed above by a solid concave plate; but this probably results from a 
thickening of the walls, or from the thickening of the exterior wall alone, the 
concave plate representing the base of the interior original cavity. The depressions 
were evidently intended for the reception of other plates, which at that time were 
entirely unknown. 
Recently I have obtained from Mr. Andrews of Cumberland, Maryland, a series 
of specimens which fully illustrate the characters of the genus so far as regards the 
plates of the body and arms, and also prove the mode of growth. By reference to 
Plate lxxxvii ( Crinoidem of the Oriskany sandstone), it will be seen from several 
examples that these crinoids are sessile in the young state, adhering singly or in 
groups to other substances until fully developed, when they are separated from the 
foreign bodies, and, gradually secreting calcareous matter to cover the cicatrix or 
point of adhesion, become finally the smoothly rounded bases Avhich we find so 
numerously in the shaly limestone of the Lower Helderberg and the Oriskany 
sandstone. 
In this progress of growth and separation, the base of the crinoid undergoes many 
modifications of form; presenting itself with the angular outlines of the recently 
attached surface, or with these angles removed, and the cicatrix in various stages 
of obliteration, until finally the base becomes smooth and rounded, but varying 
greatly in proportions of length and breadth. 
In the Oriskany sandstone, these bodies are equally as abundant as in the shaly 
limestone of the Lower Helderberg; and they not unfrequently preserve the radial 
plates at the base of the arms. 
