GENUS GOMPHOCYSTITES. 309 



descriptions relate almost exclusively to species that have been in my 

 cabinet for several years, and which were studied, and many of them de- 

 termined, at the time of making the Report above cited. 



Some of the Crinoidea are very interesting ; but the Cystideans possess a 

 peculiar interest, as offering forms which, so far as I know, have not been 

 discovered in any other localities. The specimens, with few exceptions, 

 are casts of the interior of the test, or impressions of the exterior left in 

 the matrix. A few of the species retain the plates to such an extent that 

 the structure can be determined. Since it appears probable that we shall, 

 for some time at least, be dependent upon similar imperfect materials for 

 our knowledge of these fossils, I shall endeavor to give such descriptions 

 as will enable the student to recognize the species, with the hope that some 

 of them at least will be illustrated at a future neriod 



GENUS GOMPHOCYSTITES (nov. gen.). 

 [Toii(j)og, clavus ; Kvarog, vesica.l 



Body elongate pyriform, very narrow at the base, gradually enlarging 

 above, and near the upper extremity inflated. Surface composed of nu- 

 merous ranges of polygonal plates. Apertures upon the upper surface, 

 one of them being subcentral and the other a little eccentric. 

 Arms sessile, lying in grooves excavated in the surface of the plates, 

 originating near the mouth, and, curving spirally outwards and down- 

 wards over the body, they reach to the point of its greatest diameter. 

 The central aperture has probably been closed by a pyramid of five or 

 six small plates. 



The fossils of this genus are remarkable for their elongate form, attenu- 

 ate base and swelling upper extremity : they were probably supported 

 upon a short pedicel, but we do not know its character. The body is com- 

 posed of numerous ranges of short hexagonal or polygonal plates, which 

 can be traced in their marking. 



In a fragment of one of these from the Niagara shale of New-York, 

 there is but a single subcentral opening visible, the arms all originating 

 on one side of this. In the casts of other species from Wisconsin, there is 

 evidence of a smaller aperture near the round subcentral one. 



A large proportion of the specimens observed are unsymmetrical in 

 greater or less degree, and this feature is apparently very variable in the 

 same species. In a view of the summit, the position of the apertures and 

 disposition of the arms resemble Agelacrinus ; but the plates are of 

 different character, being strongly granulose, and the sutures of the plates 

 are so close as to make it difiicult to distinguish them. 



