CROT ALO CR I N I DAE 
129 
with the radials, that the muscular articulation admitting motion begins. The systematic posi- 
tion of the genus has been dififerently interpreted by authors, and is evidently intermediate, 
pointing on the one hand to a connection with the Camerata, and on the other with the Inadu- 
nata, with the preponderance in favor of the latter. 
A more comprehensive discussion of this remarkable genus, with ample illustrations, 
may be found in Wachsmuth and Springer’s paper of 1888, entitled “ Crotalocrinus, its Struc- 
ture and Zoological Position.” ^ It contains an especially fine picture of the form having 
the reticulate rays continuous part way and inrolled from the ends, for which I have not room 
enough on my plate. The genus, although rare, is one of the most characteristic of the 
specialized forms in the Silurian of England and Gotland. 
Crotalocrinus has not been found thus far within the area embraced in this work, but 
it is liable to appear at any time, as it has been recognized in the Racine dolomite of the 
Chicago area by Weller, and recently in the Silurian of Gaspe by Schuchert, thus adding 
another significant link to the chain of connection of the American Silurian with that of 
northern Europe. Eor this reason, as well as for comparison with the other highly specialized 
Pefalocrinus, I have thought it would be of service to give some figures showing the charac- 
teristics of the type. 
Crotalocrinus cora (Hall) 
Plate 26, fig. 17 
Cyathocrinus cora Hall, 20th Rep. New York St. Mus., 1868, p. 324, pi. ii, figs. 13, 14; rev. ed., 1870, 
p. 366. — Crotalocrinus americanus Weller, Bull. 4, Chicago Acad. Sci. Nat. Hist. Surv., 1900, p. 143, 
pi. 14, fig.- I ; Crotalocrinus cora, Jour. Geol., 10, p. 532, pi. 3, figs. 1-5. — Slocom, Field Columb. 
Mus., 2, Geol. Ser., 10, 1908, p. 292, pi. 86, figs. 3, 4. — Bassler, Bibliogr. Index, vol. i, 1915, p. 292. 
This species occurs in the Racine dolomite at Racine, Wisconsin, and at 
Chicago, described at an early day but its generic affinities not recognized until 
long after. Its history and characters are fully set forth in Dr. Weller’s paper 
above cited, reinforced by further illustrations by Slocom, leaving no doubt of 
the correctness of his reference to the genus. By way of confirmatory evidence 
I give a figure of another specimen from Chicago showing an intensity of sur- 
face sculpture similar to that of the English species following. 
Crotalocrinus rugosus (J. S. Miller) 
Plate 26, figs. 18-20 
Cyathocrinus rugosus Miller, Nat. Hist. Grin., 1821, p. 89, with plate. — Crotalocrinus rugosus Austin, 
Ann. and Mag. Nat. Hist., vol. ii, 1843, p. 198. — Angelin, Icon. Grin. Suec., 1878, p. 26, pis. 7, fig. 4; 
17, figs. 8, 8a (not figs. 3, 3a, b). — Wachsmuth and Springer, Proc. Acad. Sci. Phil., 1888, pp. 364, 
386, pi. 19, figs. 1-5. 
I am figuring a calyx of this species from the type locality at Dudley, 
England, for comparison with our Chicago specimens in the matter of surface 
markings and arrangement of plates, plate 26, figure 18. There are also two 
instructive structural figures, 19 and 20, from a Gotland specimen, the first 
showing the arrangement of the lower brachials in contact with the radial, and 
the second the mode of connection between the brachials of abutting arm- 
branches with the projecting processes midway and the open spaces between 
them forming the flexible net work ; and also the covering plates of the ambulacra. 
1 Proc. Acad. Nat. Sci. Phil., Nov., 1888, pp. 364-390; pis. 19, 20. 
