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PALEONTOLOGY 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 another characteristic feature which has been described by M. Von 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 Caryockinus in the young and mature 

 " 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. 



