NIAGARA FALLS AND VICINITY 1 53 



An anal interradius is present in unsymmetric forms. The tcgiiien 

 forms the cover, or ventral part of the calyx, and is composed of 

 plates either closely ankylosed, or held together by a leathery 

 membrane. In the Paleozoic Camerata the plates of the ventral 

 disk lit closely and they are considerably thickened, forming- a very 

 rigid, more or less convex vault, from which may rise the plated 

 anal proboscis. 



The mouth of Paleozoic camerate crinoids lies beneath the teg- 

 men, the only external opening being that of the anus. From the 

 mouth/ radiating grooves or canals commonly pass outward to the 

 arms, in which they are continued. These are the ambulacral 

 grooves, along which the food, caught on the arms, is conveyed 

 to the central mouth. These grooves may be open or covered by 

 plates. Within the cavity of the calyx are the viscera. 



The stalk, or stem, is composed of a varying number of joints, 

 which are circular, elliptic or angular in cross-section (fig. 52). 

 The joint nearest to the calyx is the last formed except in the 

 Flexibilia. Frequently a certain number of the joints bear root- 

 like extensions or cirri. The stem and cirri are pierced by an axial 

 canal, round or pentagonal in cross-section. The stem was in most 

 cases attached by a root. Some crinoids were without a stem, hav- 

 ing been attached by the base directly or more rarely being free- 

 swimming: organisms. 



Order larvifor:ivii^^ Wachsmuth & Springer 

 Genus stephanocrinus Conrad 



[Ety. <7Ti(favo<$, a crown; y.phov, a lily] 



(1842. Acad. nat. sci. Phil. Jour. 8:278) 



Calyx cup-shaped, composed of three elongate basals, five radials, 

 and five interradials. Radials deeply forked; the prongs formed by 

 the margins of two continuous radials extending upward between 

 the arms, and building, together with the interradials, a row of five 

 pyramids, near the summit of one of which is sittiated the anal 

 aperture. Radial incisions occupied by the ambulacral grooves, 

 which are roofed over by two rows of covering pieces; those of the 

 same row closely ankylosed. First costals semilunate, and resting 

 within a horseshoe-like concavity near the outer end of the radial 

 incisions. Tegmen constituted of five large triangular oral plates. 

 Arms very short,^ composed of about 10 pieces, all of which are 

 axillary and give off side arms. The latter are biserial, non-pinnu- 



^ Generally wanting in the weathered-out specimens. 



