HEXACRINIDiE. 779 



difficult to make comparison with allied forms. The descriptions of this and 

 the two preceding species are made after Miller, we having no authentic 

 specimens for comparison. 



CAMPTOCRINUS W. and Sp. (nov. subgen.). 

 (Ka/xTTTo's pliant, Kpivov a lily.) 



In the construction of the calyx and arms identical with Dichocrinus, but 

 differing in the structure of the stem, which in all the specimens in which 

 we observed it is curled around the crown. The stem joints are circular 

 near the calyx, but at some distance off gradually turn into crescent-shaped, 

 and the two horns of the crescent give off long, stout, and pliant cirri from 

 every joint. The stem coils to the concave side. 



The structure of this stem reminds us of Hall's genus Myelodactijlus * of 

 the Niagara group ; and similar stems occur in the Wenlock limestone of 

 Dudley, England, and Gotland, Sweden, which have been referred by Angelin, 

 and also by Bather, to the inadunate genus Herpetocriniis Salter, a genus 

 with close affinities to Heterocrinus. Such stems are also found among the 

 PoteriocriniclcB of the Kaskaskia group, showing that they occur not only at 

 various horizons, but also in very different groups ; and we doubt if this 

 structure is of much importance for classification. We therefore place Camp- 

 tocrinus subgenerically under Dichocrinus. 



Distribution. — Found from the Keokuk limestone to the Kaskaskia group, 

 and apparently restricted to America. 



T//2ye. — Cam2otocrinus mt/elodactylus. 



Camptocrinus myelodaetylus W. and Sp. (nov. spec), 



Plate LXXV. Figs. 1, 2a, I. 



A small species with curving stem and long paired cirri, which are given 

 off in longitudinal rows on the concave side, as in Hall's Mijelodactylus. Calyx 

 elongate, slightly spreading ; the plates smooth ; the suture lines indistinct. 

 Base one third the height of the dorsal cup, its sides convex. Eadials twice 

 as long as wide ; the facets not excavated, and the costals resting upon the 

 straight upper faces, occupying three fourths their width. Costals two, very 

 short; the second obtusely angular above. Arms two to the ray, in close 

 contact laterally, twice and a half as long as the calyx, and composed of 



* Palffiont. N. York, Vol. II., p. 232, Plate 42, Tigs. 5, 6, and Plate 45, Eigs. 7, 8, 9. 



