LECANOCRINIDAE 1 67 



was not constructed for permanent attachment to other objects, but was perhaps capable of 

 being wound around them for temporary anchorage. This form of column indicates that 

 these crinoids probably floated about in quiet water, in strong contrast to genera like Calpio- 

 crinns, which with their very short, stout column and broad encrusting root, must have lived 

 in shallow water attached to the bottom and contending with currents. 



The type species was described by Worthen under Centrocrinus, and was subsequently 

 referred by Wachsmuth and Springer to their proposed genus Idiocrinus — both on the sup- 

 position that it was a Camerate crinoid. The solitary specimen then known did not indicate 

 the Flexible affinities which are so clearly established by the material now in hand. 



After this well-defined type had been recognized in the Tennessee specimens it became 

 evident that the genus was widely distributed, and would readily include certain specimens 

 from England and Gotland which had baffled all efforts to refer them to any of the known 

 genera. Thus the genus is represented by a species in each of the well-known. Silurian re- 

 gions of America, England and Sweden ; and since the accompanying descriptions were pre- 

 pared the American range of the genus has been enlarged by the discovery of a specimen 

 closely allied to the type in the Laurel formation at St. Paul, Indiana. 



The species may be arranged as follows : 



The Species of Hormocrinus 



I. IBr 2. Calyx ridges angular from RR to BB. 



RR much larger than IBr. 



Surface not pustulose. 



Columnals large, convex, strongly alternating proximally H. tennesseensis. 



RR but little larger than IAx. 

 Surface pustulose. 



Columnals short, with slight alternation H. anglicus. 



II. IBr 3 or more, calyx ridges obscure or wanting. 



Surface smooth. 



Columnals short, with slight alternation H. gotlaitdicus. 



Hormocrinus tennesseensis (Worthen) 

 Plate XIV, figs. 1-5 



Centrocrinus tennesseensis Worthen, Geol. Surv. Illinois, VIII, 1890, p. 95, pi. 14, fig. 1. — Foerste, Jour. 



Geology, XI, 1903, p. 712. 

 ? Idiocrinus tennesseensis, Wachsmuth and Springer, N. A. Crinoidea Camerata, 1897, p. 206, pi. 18, 



fig. 11. 



Type of the genus. 



Specimens rather small. Crown short, conical, broadly spreading, with 

 angular ridges marking the course of the dorsal nerve cords and passing from 

 IBB to center of BB, thence coalescing on RR and following median line of Br 

 to the arms ; spread of calyx from base to top of RR, about I to 3; height to 

 width, 1 to 2. iBr areas depressed, cross-section at IBr pentagonal. Surface 

 without ornament except the ridges. Maximum crown, 12 mm. high by 15 mm. 

 wide; base at IBB, 5 mm.; proximal columnal, 3.5 mm. 



IBB large, forming a short, convex cylindrical rim. BB about equal in 

 height to RR. Anal x with truncate apex, followed by perisome in the middle 

 and by a plate on each sloping shoulder abutting on IBn, and IBr 2 ; iBr 1 large 



