222 



PALEONTOLOGY OP NEW-YORK. 



the apertures on the exterior surface ; and again on the lower half of the plate, the tentacular 

 grooves are directed to the lower margins of the plate, leaving the ridge above them cor- 

 responding to the external ridge above the rows of pores on the lower half of the plate. This 

 arrangement of the pores often leaves a large portion of the interior of the plate, across the 

 centre, free from these tentacular grooves ; and it becomes much thickened, sometimes in 

 distinct ridges, and in other instances the ridges uniting form a thick callosity across the middle 

 of the plate. This character is very well shown in the plates, figs. Is, It, and 1 t+ . 



It should not be forgotten, however, that there are in most instances interrupted rows of 

 pores, or a few scattered ones, along the lateral margins of the costal plates, which, like the 

 others, penetrate to the interior. The tentacular grooves extending from these pores reach to the 

 lateral edges of the plate, meeting other similar grooves from the opposite side. In all the 

 examples of the interior surface of plates, the spaces not occupied by pores, or the grooves 

 extending therefrom, are filled by thickened ridges or callosities, which may or may not have 

 corresponding ridges or tubercles upon the exterior surface. The arrangement of these pores, 

 and the tentacular grooves, is well shown in the figures before referred to, and in fig. 1 m, 

 which represents the interior of one of these crinoids. 



The beautiful symmetry of all these parts, their constant presence and relations to each other, 

 show that they are intimately connected with the vital functions of the animal economy. By 

 the arrangement of these pores, and their relation to the parts of the plate, it is e^^dent that 

 the organs occupying them, and the interior structure communicating with them, performed an 

 important office in the increase of the plates, and the consequent enlargement of the entire animal. 

 Mr. Miller supposes that there was a membrane protruding between the joining edges of the 

 plates, enveloping their external surface, and producing the striae or ridges marking the plates 

 . in all the Crinoidea. If such a membrane existed in the Caryocrinus, it was probably subor- 

 dinate in its functions to the organs occupying the pores. The striae, or granulated lines parallel 

 to the margins of the plates, are usually the only evidences we have of the mode of increase 

 in the plates of the Crinoidea ; but in the Caryocrinus, we have these radiating rows of pores, 

 beginning in the younger specimens with one, two, or three pores in each row, and, as the body 

 increases in size, showing constantly that they increase by the addition of new pores on the distal 

 or marginal extremity of the rows, till they reach the number of fifteen or twenty, and this shows 

 most clearly the mode of extension by increments upon the margins of all and every one of 

 the plates individually. There is certainly no species of this family, within the range of our 

 knowledge, which furnishes so much instruction relative to the structure of parts, and mode 

 of growth of the Crinoidea, as the Genus Caryocrinus. The extravagance of some parts, 

 the modification of some, with the occasional absence of others, furnishes an instructive study, 

 and enables one to understand more readily those variations and modifications, which, though 

 occurring in other species, are rarely or never presented in such perfection, or in a manner so 

 readily to be understood and explained, as in this species. 



M. VoN BucH has shown how this remarkable crinoid differs from the true Crinoidea, where 

 the number of plates is five, or, in the pelvis, three, two of which are divisible, making five of 



