THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES. 51 



arms from 13 to 20, but* 80 per cent of them from 15 to 17; and in 

 size from 12 to 16 mm. high, and 17 to 22 mm. wide. 



Horizon and locality. — Hamilton (Sellersburg) limestone: Charles- 

 town, Indiana and vicinity. 



DOLATOCRINUS EXORNATUS Miller and Gurley. 



Plate 13, figs. 11, 12. 



Dolatocrinus exornatus Miller and Gurley, Bull. 6, 111. St. Mus., 1895, p. 54, 



pi. 5, figs. 8-10. 

 Dolatocrinus dispar Miller and Gurley, Bull. 9, 1896, p. 40, pi. 2, figs. 27-29. 



Very small, with extremely fine striae; radial ridges high and sharp. 

 The size is consistently small, being almost miiform at 8 mm. high 

 and 12 mm. wide, and the tendency is to 20 arms. Out of seven 

 specimens plus the types more than half have 19 to 20 arms, and all 

 may have had about 20, as in this form the first bifurcation of the 

 ray occurs very high up, and the next one is at the edge of the calyx, 

 where the arms are becoming free, so that the second axillary is 

 sometimes broken off and the full number of arms is not seen. 



Comparison of the original description of this species with that of 

 D. aureatus immediately following it, illustrates the method of the 

 authors. The two descriptions are verbally identical as to the essen- 

 tial characters, the only difference being that aureatus has one less 

 arm, and one more small plate in the third interbrachial range. 



Horizon and locality. — Hamilton (Sellersburg) limestone: Charles- 

 town, Indiana, and vicinity. 



DOLATOCRINUS CANADENSIS Whiteaves. 



Dolatocrinus canadensis Whiteaves, Contr. Canad. Paleont., vol. 1, 1887, p. 99, 

 pi. 12, figs. .3, 3a.— Wachsmuth and Springer, N. A. Grin. Cam., 1897, p 

 315, pi. 2.5. figs. 7a. b. 



This species, described from the Hamilton of Thedford, Ontario, 

 was founded upon a single small specimen probably somewhat 

 eroded. It seems to be of the type of D. marshi, but with 15 arms 

 instead of 10. A form somewhat similar to marshi has been noted 

 from western New York, but the material is not available for com- 

 parison. 



Horizon and locality. — Hamilton shales: Thedford, Ontario. 



Form 7. MAGNIFICUS group. 



Calyx large to medium size, occasionally small; oblate hemisphe- 

 roidal, or depressed bursiform, constricted below the arms; base 

 broadly truncate, flat, or shallow concave. Plates highly orna- 

 mented with ridges, striae, nodes, or pustules; radial series bearing 

 nodes round or elongate, either separated, or connected by a narrow 

 neck, or meeting at the sutures to form a continuous median ridge : 



