124 WELLER. 



divided portions spread outward in a nearly horizontal position, 

 occupying about one fifth of the total length of the plates. The 

 apices of each of the two adjacent radials are united to form an 

 acute point which projects a little above the summit. Radial 

 sinuses deep, the sides subparallel, elevated so as to form sharp 

 edges, the portion bounding the base of the sinus more highly 

 elevated than at other points. Deltoid plates apical, not visible 

 in a side view, except on the posterior side, where there is a 

 small rhomboidal plate. 



Ambulacra linear, narrowly rounded at the base, and but 

 little wider at the summit than at the base. Surface transversely 

 convex, forming a longitudinal depression along each side, the 

 central portion not raised to the general level of the radials. 

 The food groove along the median line of each ambulacrum 

 deepens and widens near the summit. 



Spiracles rather large, the posterior one confluent with the 

 arms. 



Surface of the radial plates ornamented with prominent raised 

 concentric ridges which converge dow^nwards towards the lateral 

 sutures. 



Remarks. This species is in man}' respects similar to the 

 last, but differs in its larger size and in its proportionally broader 

 radials and shorter base, giving to the body a fuller appearance. 

 The rounded base of the radial sinus and ambulacra is broader 

 and more obtuse in this species than in the last, and the sides of 

 the ambulacra are more nearly parallel. The concentric orna- 

 mentation of sharply elevated ridges upon the radials, is much 

 more conspicuous than in the last species, it being always easily 

 recognized without the aid of a lens. 



In the specimen figured the base is not preserved, the outline 

 indicated being taken from another specimen. 



Tpie University of Chicago, 

 January 1 8, 1898. 



