Oct., 1907. 



New Crinoids — '■ Slocom. 



281 



tion. There seems to be no reason to doubt that they are specifically 

 identical with the specimens from Tennessee on which the original 

 description was based. 



Fig. 4. Diagram of Stephanocrinus. 



Family STEPHANOCRINIDA^E. 



STEPHANOCRINUS Conrad. 



Only one species of this genus has heretofore been recognized in the 

 Chicago Area. Two new species have been collected by the writer and 

 are here described. The generic characters are as follows : Basals three, 

 about equal in size, two pen- 

 tangular, one quadrangular. 

 Radials five, equal, resem- 

 bling the forked plates of 

 some Blastoids. These prongs 

 form interradial processes, 

 and between them are situ- 

 ated the ambulacral grooves 

 leading to the arms, which 

 rise from a single axillary 

 costal plate situated at the 

 end of the sinus. Oral plates five, interradial in position and forming 

 most of the ventral disc. They are not visible in a side view of the 

 calyx. They join the inner surface of the radial plates and extend to 

 the top of the interradial processes. Their lateral edges are in contact 

 below the ambulacral grooves, but a space is left for the mouth at the 

 center of the ventral disc. The anus is situated between the posterior 

 oral plate and the adjoining process. 



This genus has been referred to the Cystoids and Blastoids by some 

 writers, and while it undoubtedly has some characters similar to both 

 it has been shown to be a Crinoid by Wachsmuth and Springer on 

 account of its brachial plates. » 



Stephanocrinus obconicus sp. nov. Plate LXXXIV, Figs. 12, 13. 



The dorsal cup is obconical, truncated at the base, sides slightly con- 

 vex, forming an angle of about 30 degrees. The surface of the plates 

 is apparently smooth or finely granulose, following the curve of the 

 calyx except near the proximal end of the basal plates, where they de- 

 velop a median ridge giving a triangular form to the base. This ridge 

 is most prominent at the base and rapidly diminishes, disappearing 



