138 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



Interradial series consisting of three or four plates arranged one 

 above the other : the first very large, heptagonal; the second 

 pentagonal or hexagonal; the third and fourth small; the upper 

 one is placed between the arm-bases. Dome-plates numerous, va- 

 riable in size and form. 



Arms two from each ray, unknown except near the base. 



Surface of plates not rising above the general convexity of the 

 body, except a strong sharp carina or ridge which traverses each 

 ray from the edge of the basal depression to the base of the free 

 arms, bifurcating on the third radial plate : this carina is strongest 

 at its origin and on the second radial plate. 



Geological fomiaiion and locality. In the limestone of the Tipper Hel- 

 derberg group : Schoharie, and elsewhere in New- York. 



CACABOCRINUS TROOSTI (n.s.). 



Body of medium size. Calyx subheraispherical, moderately depressed 

 at the base. Basal plates a little more in diameter than twice that 

 of the column. First radials wider than high. Second radials 

 quadrangular, twice as wide as high. Third radials short and 

 broad, pentangular, a little larger than the second; supporting 

 upon each upper edge a series of two supraradials; the upper one 

 wedgeform above, and giving origin to an arm on each side. 



First interradial plate equal to or larger than the first radial, ten- 

 or eleven-sided, irregularly subovate; supporting two or three 

 small elongate plates above, which are followed by another range 

 of still smaller plates between the arms of the adjacent rays. 

 Intersupraradials, one between the main divisions of the ray. 



Arms long, slender, round on the back, composed of a single series 

 of joints which are about once and a half as wdde as high. Each 

 plate bears upon the lateral edges long slender jointed tentacula. 

 The arms are four from each ray at their origin, bifurcating twice 

 and sometimes three times above. , , 



From the middle of the first radial plate to the origin of the 

 free arms, the plates of this series are traversed by an abruptly 

 elevated rounded ridge. The surface of all the calyx-plates marked 

 by radiating and parallel lines of granulse. Longitudinal confluent 

 striae mark the arms in well-preserved specimens. 



This species differs from the preceding in the form of body, iu the 

 surface markings, and in having the basal plates external to the column- 

 facet. 



Geological formation and locality. In the shales of the Hamilton group: 

 Western New- York. C. A. White, collector. 



