164 PALEONTOLOGY OF OHIO. 



Surface of plates usually strongly nodose, becoming sub-angular or 

 ridged towards the margins. 



Column comparatively strong, composed of very thick, unequal joints, 

 the larger ones being angular on the periphery, and sometimes showing 

 a tendency to produce small nodes. 



This species is of the type of A. unicornis, of the Burlington limestone, 

 and is nearly related to A. prsecursor, of the Hamilton group ; but that 

 one has a stronger body and more robust arms, with but three arms from 

 each ray. It may also be compared with A. cauliculus, of the Hamilton 

 group, which has a smaller and less spreading base, with more numerous 

 and less spreading arms. 



Formation and locality: In shales of the Waverly group, at Richfield, Summit 

 county, Ohio. 



AcTiNOCRiNUs Ems. 



Plate 11, figs. 9, 10, 

 Actinocrirms helice, var. Eris; 17th Rept. on the N. Y. State Cab. of Nat. Hist., p. 53. 



Body short and broadly turbinate, somewhat lobed at the divisions of 

 the rays. Basal plates small, slightly projecting at their lower margins; 

 first radial plates proportionally large, wider than high ; second radials 

 small, quadrangular ; third radials larger than the second, wider than 

 high, very obtusely wedge-form above, supporting brachial plates in the 

 anterior and antero-lateral rays, giving two arms to each ; in the postero- 

 lateral rays the third radials support supraradials on the anal side and 

 brachials on the other side, giving three arms to each of these rays. 



This structure gives a formula of 



21=12 arms. 



33 



■ Interradial areas small, the first plate large, heptagonal or octagonal, 

 with one or two plates above. Anal area large, the first plate large, hep- 

 tagonal, supporting three smaller plates in the second range. 



Arms proportionally large and strong, composed of a double series of 

 short, interlocking plates, which are ridged transversely. Plates of the 

 body depressed convex, sub-angular in the upper series. 



This species corresponds with A. helice in general form and propor- 

 tions, but the plates of the body are not nodose, and the arm formula 

 differs conspicuously, there being in this but three arms to each of the 

 postero-lateral rays, while that has four. Prom this constancy of char- 



