332 PROCEEDINGS OF THE ACADEMY OF [1881. 



20. STROTOCRINUS Meek and Worthcn. 



(PI. 18, figs. 1, 2.) 



1806. Meek and Worthen (in part, Sect. A). Geol. Rep. 111., ii, p. 188. 



1866. Meek and Woithen. Proc. Acad. Nat. Sci. Phila., p. 253. 



1869, Meek and Worthen. Ibid., p. 158. 



1873. Meek and Worthen. Geol. Rep. 111., v, p. 347. 



1878. Zittel. (Subgenus of Actinocr.) Handb. d. Palaeont., p. 370. 



Syn, Actinocrinus (in part) Hall, 1860 and 61 ; Meek and Worthen, 



1861. 

 Syn. Calathocrinun 'Ksl\. (Subgenus of J.c<i»(?mwM8.) 1861, Desc. 

 New Sp. Crin., p. 13 (not von Meyer, 1848). 



The relations of this genus with Teleiocrinus — Meek and 

 Worthen's Strotocrinus B — have been sufficiently discussed, also 

 with Physetocrinns, and so we offer without remarks our 



Revised Generic Diagnosis. — Body extremely large, the lower 

 portions conical, the upper spread horizontally, forming a con- 

 tinuous rim surmounting the cone ; dome flat or slightly convex, 

 without anal tube ; surface of plates beautifully striated. 



Basals three, large, of equal size, forming a cup which is 

 truncate below. Primary radials 3X5; the first larger, higher 

 than wide ; second and third of nearly equal size. The third 

 radials give off 1X2X5 secondary radials, all bifurcating plates, 

 which form the bases of the two main divisions of the ray. 

 These and all succeeding plates are spread out horizontally, and 

 form a part of the rim. 



The succeeding orders of radials are composed of 1 X 2 plates 

 to each main division of the ray, one of them alwa^^s axillary, the 

 other truncate above. The former gives off the next number of 

 radials, while the latter is succeeded by a number of fixed arm 

 plates which form lateral branches and give off finally the free arms. 

 The radials are so arranged that in each succeeding order, and 

 these are numerous, the bifurcating plate is placed always to the 

 opposite side, so that the branches are given off alternately from 

 opposite sides like pinnules. The two main trunks of each ray 

 extend in length beyond the branches, and as both, the main trunks 

 and branches, are marked along the median line by a conspicuous 

 ridge or elevation, passing from plate to plate, the branching of 

 the rays in the rim is most beautifully indicated. In the forma- 

 tion of the rim, the interradial and interaxillary plates also con- 

 tribute, and these extend frequently to near the free arm bases. 



