208 Twenty-fourth Report on the State Museum. 



radial, above which the plates are smaller and soon become free, 

 forming the bases of the arms. Interradial series, consisting of six 

 or more plates, varying from pentagonal to heptagonal. Intersupra- 

 radials, one, two or more. 



Arms long, slender, composed of a single series of short, slightly 

 wedge-form plates, supporting tentacula on the sides of the alternat- 

 ing plates; tentacula long and comparatively strong. 



Surface of plates smooth ; the center of those composing the rays 

 strongly elevated, forming a strong round ridge along the ray to the 

 arms. 



This small specimen bears very close resemblance to G. decadac- 

 tylus Hall, and may possibly prove to be the young of that species. 

 In its present condition it is not so broadly turbinate as the young 

 individuals heretofore seen of that species. 



Formation and locality. In rocks'of the Hudson-river group at 

 Cincinnati, Ohio. 



Genus — POTERIOORIJSrUS Miller. 



Subgenus — Dendrocrinus Hall. 



PoTERiooKiNus (Dendroceinus) caduceus n. sp. 

 Plate 5, figs. 7, 8. 



Calyx of medium size, regularly turbinate, lobed at the arm-bases 

 by the projection of the upper part of the first radial plates. 



Basal plates elongate, pentagonal, the upper ends very obtusely 

 wedge-form. Subradial plates higher than wide, four hexagonal and 

 one heptagonal. First radial plates wider than high, the upper 

 margins deeply excavated for the reception of the first arm plate. 

 Anal series consisting of one large hexagonal plate resting upon the 

 upper end of the heptagonal subradial plate, supporting other smaller 

 plates above ; three ranges are visible in one individual, the central 

 range largest and gradually diminishing in size upward ; twenty -four 

 or twenty-five plates can be counted in direct succession ; they are 

 hexagonal, with an elevated ridge along the middle of the range. 



Surface of body plates obscurely marked by radiating ridges, which 

 are more distinct near the sutures where they unite with those from 

 the adjoining plates ; the lateral edges of each plate are marked by 

 two or three of these ridges, while tlie other margins have one each. 



Arms composed of a single series of short plates, and frequently 

 bifurcating, the first division on the sixth above the first radial plate. 

 The arms are of moderate size at their origin, rapidly diminishing at 



