

232 PROCEEDINGS OF THE ACADEMY OF [1879. 



No such organs have ever been described in the true Crinoids 

 neither from the Palseocrinoidea nor the Pentacrinidae. 



We have given so minute a description of the hydrospires as 

 they occur in the C\ r stideans and Blastoids, partly because they 

 have been indifferently known, but also in order that we may bet- 

 ter compare with them certain organic structures, which we have 

 discovered in some Paleocrinoids, and which we think still further 

 distinguish the latter from recent Crinoids, while at the same 

 time indicating a closer relationship with the Blastoids and 

 Cystideans. 



Wachsmuth, in Am. Journ. Sci., Aug. 1871, p. 126, noted a 

 marked difference between the proboscis in the Actinocrinidse and 

 that in the Cyathocrinidae. He considered the former a mere 

 anal tube, or prolongation of the anal opening; but this organ in 

 the Cyathocrinidae he believed to be an essential part of the body, 

 in which the anal opening, here located laterally and low down, is 

 of but secondary importance, and therefore proposed to call it 

 " ventral sac" instead of proboscis. We have since had occasion 

 to examine the ventral sac in several most excellent specimens, 

 particularly with reference to the pores to which he called atten- 

 tion, and have become convinced that these are very probably the 

 homologues of the calycine pores in the Cj'stideans. The plates 

 of the ventral sac in the Gyathocrinidae are usually comparatively 

 large, rather thin, hexagonal pieces, longitudinally arranged, alter- 

 nating with those of the adjoining rows. The pores perforate the 

 plate at each angle. It is now very interesting to observe that in 

 some species for instance, Poteriocrinus 31issouriensis, Shum. 

 Pot. (Scaphiocrinus) unicus Hall, there are in place of the pores 

 slit-like fissures of considerable length. Four of these fissures 

 sometimes six connect with those of the plates of the adjacent 

 row, those of each half of a plate meeting corresponding slits in 

 two different plates, so that one half of the fissures point upward 

 and the other downward. We have filed several of the plates to 

 the very bottom, and have found that the fissures pass entirely 

 through them, and in many cases, where they have been observed, 

 they form longitudinal depressions along the ventral sac, caused 

 bj' the thinning of the plates toward the fissures. In some species, 



that they form excellent generic distinctions. It is really astonishing how 

 beautifully in some instances, these delicate organs have been preserved. 



