l66 SMITHSONIAN INSTITUTION 



HORMOCRINUS nov. gen. 



(6pj.iog, necklace; xpivov, lily) 



Plate XIV 







CZ3 



Fig. 16. Hormocrinus 



Lecanocrinidae with rays above radials partly separated by solid plates 

 followed by perisome. Crown low; calyx well differentiated. IBB erect, taking- 

 part in the calyx wall. No radianal. Anal x truncate, succeeded by smaller 

 plates abreast, or by perisome direct. Interbrachial areas wide, occupied by one 

 large plate, with or without others succeeding. Primibrachs usually 2, excep- 

 tionally 3 or 4; first one filling distal face of radial. Arms dichotomous; rays 

 arching over interbrachial areas but not interlocking. Column large, tapering 

 to a fine point, without attachment. 



Genotype. Centrocrinus tennesseensis Worthen. 



Distribution. Silurian; United States, England and Gotland. 



This genus is proposed for the reception of a fine series of specimens from the Browns- 

 port formation of western Tennessee, and some allied forms from Europe, which could not 

 be brought under any other heretofore known. While superficially resembling Pycnosacais 

 in general habitus, it is broadly distinguished from that genus by the absence of a radianal, 

 and by the presence of a large, solid interbrachial plate abutting on the first primibrach so 

 that the latter plate fills the entire distal face of the radial, shutting it off from possible con- 

 nection with perisome. This interbrachial may be followed by a few smaller plates, usually 

 only at the shoulders next to the primibrach, or by perisome directly without the interposition 

 of other plates. Like Pycnosaccus, it is subject to exception as to the number of primibrachs, 

 which is normally two and nearly constant for the American and English species, but greater 

 and irregular in the single known specimen representing the genus in Sweden. 



Hormocrinus ought not to be confused with any other genus. Those of the family which 

 are morphologically parallel to it in the absence of a radianal are thoroughly differentiated 

 by other characters. The column in the typical form is peculiar for the small amount of alter- 

 nation in the columnals, and for its very gradual taper to a small, unbranched, distal end ; it 



