222 SMITHSONIAN INSTITUTION 



LITHOCRINUS Wachsmuth and Springer 

 Plate XX, figs. 1-3 



Lithocrinus Wachsmuth and Springer, Revision Palaeocrinoidea, pt. i, 1879, p. 52; ibid., pt. 3, 1886, 

 p. 145.— Von Zittel, Grundziige Pal., 1895, p. 138. — Zittel-Eastman, Textbook Palaeontology, 1896, 

 p. 164 (2d Ed., 19,13, p. 204). — Bather, Rep. British Assoc, for 1898 [1899], p. 923; Treatise on 

 Zoology (Lankester), pt. 3, 1900, p. 189. — Springer, Amer. Geologist, XXX, 1902, p. 95; Jour. 

 Geology, XIV, 1906, p. 515. 





oP*^ 



»y en Q 



Op r=\ Q^q 



OpC3 



Fig. 25. Lithocrinus 



Sagenocrinidae with rays above radials separated all around by inter- 

 brachial plates in lower part. Crown elongate. Infrabasals recumbent, taking 

 small part in calyx wall. Radianal only in upper oblique position. Anal and 

 interbrachial areas filled with solid plates in more than one series in lower part, 

 followed by perisome passing into the tegmen. Primibrachs two. Arms heter- 

 otomous, divergent ; rays in ten main divisions with branching ramules. Column 

 large, cylindrical, not alternating at the calyx. 



Genotype. Forbesiocrinas divaricatus Angelin. 



Distribution. Silurian ; Gotland, Sweden. 



This genus, as now defined, contains the species remaining after the removal of Litho- 

 crinus obesus under the name Cholocrinus. Proposed by Wachsmuth and Springer as a sub- 

 genus to include the Silurian species described by Angelin under Forbesiocrinus, its generic 

 distinctness is well established and it may be better defined than we supposed at that time. 

 We did not designate any type species, but this was supplied in 1899 by Bather, who pro- 

 posed to restrict the genus to the type of L. divaricatus. The absence of a radianal and the 

 presence of solid interbrachial plates in the lower part of the areas differentiates it sharply 

 from Cholocrinus, to which it bears a superficial resemblance in the arm structures. The 



