128 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



from the centre of each one. The spines from the radial and in- 

 terradial plates are as long as the height of the body : the spines 

 of the subradial plates of similar character. 



The second and third radials are marked by a longitudinal ridge, 

 which bifurcates on the upper plate. The interradial plates are 

 marked by central ridges, with defined ridges extending to the 

 margins of the plate. The first radial and first interradial plates 

 are broadly undulating; the elevated parts extending from the 

 sides of the plate^^and the depressions towards the angles. Arms 

 elongate, subcylindrical, composed of short joints which are 

 narrowly grooved on the inner side, and furnished with jointed 

 tentacula. 

 Tins little species is most remarkable in the strong elongate spines, 



which are much more extreme than in any species heretofore observed. 

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



Ontario county. C. A. White, collector. 



GENUS TREMATOCRINUS (Hall). 



TRE^rATOCRINUS SPINIGERUS (n. s.). 



Body small, urnshaped, inflated in the lower part, constricted above 

 the middle and again spreading at the top, forming a rim-like 

 expansion at the base of the arms. Summit concave : base im- 

 pressed; the cavity embracing the basal and subradial plates. 

 First radial plates large, forming the base of the cup : plates of 

 the antero-lateral and postero-lateral rays uniting with each other 

 by the lateral edges; the others separated by the first interradial 

 and first anal plates of the corresponding areas, w^hich truncate 

 and rest upon the subradials. Second radials but little smaller 

 than the first, hexagonal. Third radials smaller than the second, 

 heptagonal; the upper cuneate edge supporting the superradials, 

 from the second of which rise the true arms : these are long and 

 slender, rounded on the back, and in the lower part consisting of 

 short plates, bifurcating on the fifth plate; above this, they are 

 composed of short cuneiform plates, arranged like those of true 



POTERIOCRINUS. 



Interradial spaces occupied by fifteen or sixteen small plates, and 

 enclosed at the top by the summit-arms, which are proportionally 

 strong in the lower part and composed of a double series of semi- 

 elliptical plates to the fourth pair, where they bifurcate, forming 

 a pair of sl4nder cylindrical processes. The entire length of these 

 arms is about one-fourth greater than the height of the w^hole 

 body. 



