LOWER HELDERBERG ROCKS. 
99 
CRINOIDEiE AND CYSTIDEiE OF THE LOWER HELDERBERG LIMESTONES AND 
ORISKANY SANDSTONE*. 
Upon the commencement of the engraving for the third volume of the 
Palaeontology of New-York, not more than five species of Crinoidese and 
Cystideae were' known to occur in these rocks. The great numbers of 
columns and other fragments of these fossils in certain localities induced 
a belief that a greater number of species would eventually be found ; and 
a much larger number of plates was assigned for the illustration of these 
fossils, than would have been required for those at that time known. 
As the collections have progressed, new species have at intervals been 
discovered, and also better specimens of those previously known ; so that 
although the material for the illustration of these families of fossils was 
formerly so meagre, we have now the means of presenting an interesting 
group. The species and individuals are far from being as numerous as 
those of the Niagara group ; and while a single crinoid and one cystidean 
only are of the same type, the remainder present a much wider departure 
from those, than might have been anticipated from the similarity of the 
sediments, and the affinities of the brachiopoda, corals, and bryozoa of 
the two periods. 
Notwithstanding these additions of species in the limestones, there 
still remain numerous fragments of columns, arms, etc., which are yet 
unidentified. Some fortunate localities will hereafter, probably, furnish 
as many more species as we now possess; and, judging from the limited 
range of most of the known species, we may anticipate a greatly in¬ 
creased number, when the formation shall have been thoroughly studied 
from its best known localities in New-York, along its line of outcrop to 
the southwest as far as Middle Tennessee. * 
* Corals and Bryozoa of the Lower Helderberg Limestones. The conspicuous Corals of this period 
consist of Streptelasma, Zaphrentis, Favosites, Stromatopora, Chcetetes, etc.; while the Bryozoans present 
numerous forms of Fenestella, Trematopora , Callopora, etc., which closely resemble Niagara species. 
Conceiving that it would be more satisfactory to publish the Corals and Bryozoa of this and the succeeding 
groups of strata altogether, I have made arrangements to give the descriptions and figures of all these in 
the last volume of the Paleontology of Neiv-York. 
