CRINOIDS AND BLASTOIDS. 171 



are placed over the four regular sides, and two over the azygous 

 one. \vith a radial dome plate interposed above each of the postero- 

 lateral rays. The arrangement of these plates is not correctly 

 represented in The figure. In two of our specimens, the ventral 

 covering of the arms is beautifully shown for quite a distance. 

 It consists of two rows of rather robust covering -pieces, form- 

 ing a well defined ridge, and there is at each side of them a some 

 what smaller row of side pieces. These four rows commence at the 

 edge of the vault, being continuous with it, and extend ap- 

 parently to the full length of the arms. It is the first instance, 

 to our knowledge, that side pieces have been observed in the 

 Camerata. 



Column large, round, composed of alternate thicker and thinner 

 joints, with a large pentalobate axial canal, in which the lobes, 

 instead of being rounded, are angular. 



Geological position, etc. : The same as in the last species. 



Collection of Hon. D. Arnold, and our own. 



MEGISTOCRINUS PARVUS (nov. sp.) W. & Sp. 



PI. XV. Fig. 7. A fine specimen with arms and column. (One of the rays has excep- 

 tionally but two primary radials.) 



A comparatively small species. Calyx bowl-shaped, with con- 

 vex sides, swelling regularly from the basals up. Arms long. 

 This species differs from the preceding one in the form of its 

 calyx, which is not impressed at the bottom, and in having 

 longer arms and a smaller column. Calyx plates convex, without 

 ornamentation; the suture lines well marked. The only two 

 specimens known to us are light in color. 



Basals closely anchylosed, forming a low. almost flat disk. 

 Primary radials large, decreasing in size upwards. Secondary 

 radials 2x2x5. supporting ten primary arms. Arms biserial from 

 their base up. constructed of comparatively long pieces, longitu- 

 dinally arranged, the plates- alternating. The arms are long, 

 heavy, but decrease in size after each bifurcation. The two 

 proximal arm-plates, although regularly interlocking, form 

 generally a part of the calyx. Pinnules rather strong, composed 

 of joints twice as long as wide. 



