234 
PALAEONTOLOGY OF NEW-YORK. 
In addition to these peculiar and characteristic organs, there are, in several genera at least, 
others, which have sometimes been termed u ambulacral openings ,” but which Prof. Forbes 
terms u pectinated rhombs These organs are arranged in pairs (each pair forming a rhomb [7] ) 
on contiguous plates, and have a general similarity to each other, but they are by no means 
precisely alike. They consist of a more or less elevated border or rim, which is quite thick 
and strong, evidently intended for the protection of the enclosed part, and the centre is de¬ 
pressed below the surface of the plate. In the bottom, these spaces are marked transversely 
(which is usually in a line nearly vertical to the body) by slender bars, with interspaces equal 
to the bars, from which they are termed pectinated. It is certain that these organs offered 
a means of communication between the interior and the exterior, perhaps not unlike that 
afforded by the pores of Caryocrinus and Hemicosmites ; but the dissimilarity of the indi¬ 
viduals of each pair, on adjoining plates, and their distribution in three parts of the body 
only, indicates that their office was not so universal, and probably more specific than that of 
the pores. Nevertheless these apertures open upon the interior precisely as upon the exterior ; 
and from the base of each, to the margin of the plate between these pairs of organs, there 
extend little grooves. In the other direction, the grooves are marked for a short distance at 
least; but the specimens examined do not furnish positive evidence that they extended to the 
margin of the plate* *. 
In their external form, these pectinated apertures, as just remarked, are similar, but not 
“ dorsal pole of the cuticular skeleton. Diametrically opposite to the orifice for the pedicle is placed the buccal orifice, 
“ and generally close to it is the subcentral anal orifice. The cup differs, however, from that of the crinoids, by 
“ such a predominance of the dorsal side over the ventral, that the latter is often reduced to a minimum, consisting 
“ only of the orifice of the mouth, so that the arms appear to be much nearer to the mouth than is the case with 
“ crinoids” (Volborth on the Arms of CystideiB : Trans. Min. Soc. of St. Petersburgh, 1845-6, p. 167). 
There is certainly reason to regard this argument in reference to the structure of these bodies, and the origin of 
the arms, as compared with the true Crinoideae. In the Caryocrinus, we observe in a remarkable degree the de¬ 
velopment of the dorsal side, with a diminution of the ventral, particularly in young specimens, where the summit 
is proportionally narrower than in older ones. This body is provided with true arms and tentacula, while Hemicos¬ 
mites, which is so nearly related in structure, ambulacral pores, etc., has the summit protruded, and a lateral or 
posteal ovarian aperture. The examples of Caryocrinus where the mouth is forced downwards by the absence of 
the scapular plates, or the modification of the costal plates leaves that organ much in the position, and having the 
appearance of an ovarian aperture. In the absence of arms, therefore, the Caryocrinus would become a true 
Cystidean, with the exception of the mouth. Among the analogies of Caryocrinus to the Cystideans, may be 
noticed the tentacula, which are composed of a double series of joints, alternating with each other precisely like 
the arms of Cystideans, and unlike the tentacula of any other crinoid which has fallen under my observation. It is 
not probable that Caryocrinus is the only form where intermediate characters will be found; and we shall pro¬ 
bably find a necessity of restraining subdivisions within narrower limits. 
* Prof. Forbes will pardon me for differing from his opinion in reference to these organs being media of communi¬ 
cation with the interior. I am quite sure he could not withhold his assent to this opinion, were he to examine the 
specimens I have before me. Moreover I can not conceive it possible that such conspicuous organs, and so peculiarly 
arranged with reference to the animal, and the exsert parts to the protection of the interior, should be only modifica¬ 
tions of a plate, or a metamorphosis of any part, except to serve some very important function in the animal economy. 
It is not impossible but these narrow spaces may become obsolete by coalescing of the bars, as do the pores in 
Caryocrinus; or that in the process of mineralization of the specimen, the spaces may have been filled with 
crystalline matter, taking the same character as the adjoining, originally solid, parts. 
