136 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



MEGISTOCRINUS ONTARIO ( n. s.). 



Body ratlier large, broad cupshaped. Dome depressed-convex, with 

 a small subcentral proboscis situated a little nearer the anal side ; 

 composed of numerous small polygonal plates, which are raised 

 in low rounded ridges, commencing about midway between the 

 proboscis and the margin and extending to the inner side of the 

 arm-bases, one to each division of the ray, becoming stronger 

 towards the margin. These ridges are ornamented by small spines, 

 of which there are three to the anterior ray and each of the 

 postero-lateral rays, and one to each of the antero-lateral rays, 

 and a central one just anterior to the proboscis. 



Ease flattened : basal plates small, barely extending beyond the 

 circumference of the column. Plates of the primary radial series 

 subequal or slightly diminishing in size from below upwards, 

 somewhat elongate; the third one supporting supraradials on each 

 upper face, with brachials on each of the upper sloping faces in 

 the anterior and postero-lateral rays; while in the antero-lateral 

 rays, they sustain brachials, giving only two arms to each of these 

 rays and four to each of the others, making an arm-formula 



f-f = 16 arms. 



Interradial spaces consisting of eighteen or twenty plates each : 

 there are from one to three small interbrachial plates between 

 each division of the rays. Anal plates numerous, from thirty-five 

 to forty : the first nearly as large as the first radial plates, sus- 

 taining three smaller ones in the second range and five in the 

 third; above which, they are not so regularly arranged. 



Surface of plates marked by fine radiating confluent striae, which 

 give a beautiful sculpturing to the centres. The plates of the calyx 

 are depressed. 



Arms at their base strong, composed of a double series of inter- 

 locking plates. Column round, strong, with very unequal joints. 



This species differs from the preceding in the greater depth of the 

 calyx, the more elevated and less deeply grooved dome, and in the more 

 numerous and smaller spines. It also possesses a subcentral proboscis, 

 instead of only a prominent anal aperture. The sculpturing of the plates 

 is of a different character, and the surface of the plate depressed with 

 prominent margins almost the reverse of M. depressus. 



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

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



