220 
PALiE ONTOLOGY OF NEW-YORK. 
junction of the plates above them, there extends from the centre a double row of pores ; and 
to each of the lower angles, meeting the lower angles of the scapular plates, there is a single 
row of pores directed. The double rows of pores on the costals diverge, as it were, into two 
single rows, extending from the lower lateral angles of the scapular plates to the centre ; while 
the single rows of two adjoining costal plates unite in a double row upon the angle at the base 
of the scapular plate, and extend to the centre. This very symmetrical marking gives a beautiful 
appearance to the surface of this crinoid, the ornament appearing as if arranged in fanciful 
festoons from the centre of the scapular plates to the angles and the centres of all the plates below. 
In addition to the regularly arranged rows of pores, there are usually a few others near 
the lateral margins of the costal plates, either arranged in lines parallel to the edges, or irregu¬ 
larly scattered near that part of the plate. The uses of these in this place will be seen when 
we trace the communication of the pores to the interior. 
These pores are, as described, usually minute, circular openings, being either simple perfora¬ 
tions through the plates, or having a raised border, which sometimes forms a little papulous 
elevation, having the pore at the summit. In addition to this character of the pores, there is 
another very remarkable structure observable in some of them : instead of a simple pore, we 
observe two, three, four, five, six or more, decreasing in size as the number increases; some¬ 
times there is a single one in the centre and others arranged around it, the whole penetrating 
what appears like a porous or spongy tubercle upon the surface of the plate. In many well 
preserved specimens these pores appear like minute vesicles, scarcely perforated at their 
summits, and having about the same size as the granules covering the surface of the plates 
between the rows of pores. This character is more conspicuous in the scapular plates, where 
it almost always exists to some extent. In the pelvic plates it is likewise very frequently 
present, and is not unfrequently observed on the costal plates*. This characteristic is more 
fully developed in older specimens; but in very young specimens, I have found the pores on 
the scapular and pelvic plates with double and triple perforations; and in one specimen not 
larger than a small pea, the pores of the scapular plates, though only three or four in each one, 
are some of them elongated, and others with a double perforation. In the larger and older 
specimens, the rows of vesicular tubercles marking the single rows of pores have continued to 
enlarge till they have coalesced, forming a vesicular ridge; and the double rows down the 
middle of the plate, form a broad flattened ridge with a slight depression along the centre. 
Connected with the rows of pores, particularly on the costal plates, and often on the other 
plates also, there is smother characteristic feature which has been described by M. Yon Buch, 
who, after speaking of the arrangement of the rows of pores, and other surface ornament, says : 
“ Such is the decoration of the external surface of the Cab.yocb.inus in the young and mature 
u state; but with age, it exhibits a remarkable change. Along each row of pores there arise 
* I am aware that M. Von Buch says that these vesicles do not exist on the lateral or costal plates; but I have 
in my possession many specimens in different stages of growth, where this characteristic is conspicuous, more par¬ 
ticularly in the isolated lines or irregularly scattered pores near the lateral margins, and also in the rows diverging 
from the centre. 
