350 Association of American Geologists and Naturalists. 
attested by their comminuted remains, which in some places constitute 
thick masses of limestone. They are likewise scattered throughout the 
calcareous shales, and commenced their existence at a very early period 
in the earth’s history, and their remains are found in greater or less abun- 
dance, from the calciferous sandrock through all the formations of the 
New York system. 
In the lower rocks, these remains, with one or two exceptions, are so 
far obliterated as not to be referable to their appropriate genera. It is 
not until we reach the rocks of the Niagara group, that we find them 
in any degree of perfection. In the finely comminuted homogeneous 
mud deposit forming the lower member of this group, these animals 
flourished in great numbers and equal perfection. ‘There are in this 
group more ascertained species than in all the rocks of New York be- 
sides, no less than nine being already established. Several of these 
are of genera unknown elsewhere, and are therefore interesting from 
their unique character. 
Here followed a description with figures and specimens illustrating 
the structure of the Caryocrinus ornatus, the Hypanthocrinites decorus 
and H. ceelatus, the Cyathecrinites pyriformis, and several other species. 
Some of these were exceedingly beautiful and delicate in their structure. 
Several other forms from the Hamilton, Portage and Chemung groups 
were also exhibited, some of them of great beauty and perfection. 
In their geological range, these fossils appear to be more limited than 
any other forms; and so far as my observation extends, not a single 
form is known. to extend beyond the rock or group of which it is typi- 
cal. Their fragile nature appears to have been such, that they were 
unable to withstand any great changes in the condition of the ocean bed, 
and when a quiet deposit is succeeded by one made in a more disturbed 
sea, they seem all to have perished. This was shown in the Niagara 
group, in the transition from the calcareous mud to limestone. 
In all the distinct masses forming the Helderberg series of limestones, 
we find these remains to change with the commencement of a new de- 
posit ; and though often only fragments occur, they are yet sufficiently 
characteristic. When the shales of the Hamilton group succeed these 
limestones, we find a new and distinct creation of these animals, differ- 
ing from those of the rocks below. Among these are many beautiful 
forms, though they are for the most part imperfect. In this group com- 
mences the Pentremite, and an allied genus, the Nucleocrinus. 
In the Portage and Chemung groups of rocks, these remains are like- 
wise entirely different from any of those below, and different from each 
other. ‘Though the materials of the two groups are similar, there are 
no remains continued from the lower to the higher. 
