142 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



organ has been observed in Bhizocrimis, Bathycrinus, and Holopus, and it 

 existed probably in the other genera. Among Jurassic and Later fossil 

 Crinoids, axial canals, piercing the body of the calyx plates, are known to 

 exist in the Apiocrinidas and Eugeniacrinidas (Holopidas Jaekel), and they 

 are readily recognized in the Triassic Encrinus, in some of the later Palseo- 

 zoic Poteriocrinidae, and in Mycocrimis and Catillocrinus ; but we have found 

 no trace of them in the Camerata, except in Steganocrinus pentagonus (Plate 

 LXI. Fig. 3), in which, so far as observed, the five or six proximal plates of 

 their tubular appendages are pierced by a canal. Such canals occur upon 

 the radials in some of the Cyathocrinidae, the Cupressocrinidae and Gastero- 

 comidae, and we may suppose that a chambered organ existed in these and 

 other groups, if not in all Crinoids. In cases where grooves or canals for 

 the reception of cords are not apparent, the cords ma}/ have rested against 

 the inner wall of the plates. 



B. The Convoluted Organ. 



In the abdominal cavity of Paleozoic Crinoids, the only organic structure 

 that under very favorable conditions has been observed, is a peculiar skeleton 

 which occupies the greater part of the cavity. 



It is a large convoluted body, in its outlines resembling the shell of 

 a Bulla, open at both ends. Its upper part rests directly beneath the origin 

 of the ambulacra, the lower end within the basal ring without touching the 

 plates. It is dilated above, contracted below, its lateral faces placed parallel 

 to the inner walls of the calyx; the bottom truncated. In some species it is 

 subcylindrical, wdth the vertical axis the longer, in others globose or even 

 depressed globose. In coiling around its axis, the partition walls do not 

 meet each other, but leave more or less wide interspaces. The convolutions 

 vary in number from 2 to 4 according to species, and are, as they pass out- 

 ward, directed from right to left. The walls in the usual preservation are 

 thick, and perfectly solid, as they were described by Hall; but in transverse 

 sections they frequently appear as if composed of two partitions closely fitted 

 together, and closed along the edges. In some specimens, however, the 

 walls are simple, and constructed of an extremely fine and delicate filigree 

 work, composed of minute pieces or bars, with intervening meshes, which 

 do not intersect at any uniform angle, but anastomose so as to impart a kind 

 of irregular regularity to the form and size of the meshes. No such structure 

 has ever been observed in the other specimens, in which the pores or meshes 



