110 CLEIOCRUSTUS. 



Cleiocrinus regius Billings. 



Calyx elongate conical, gradually expanding from the base to near 

 the top, where it is slightly contracted ; plates flat and without ornamen- 

 tation, except longitudinal ridges following the brachial series into the 

 arms. Infrabasals large and strong, invisible exteriorly; standing ver- 

 tically upon the edge of the column, widest and thinnest above, succeeded 

 directly by the first primibrachs; they have a shallow groove at the 

 middle of the upper edge. Basals pentagonal, truncate below and angular 

 above, except the posterior one, which is quadrangular, with perhaps 

 a slight sloping at one corner; they lie between the radials, forming with 

 them a horizontal ring of ten plates, which envelop the infrabasals by 

 their dorsal surfaces and conceal them from view ; they also project 

 downward over the column for a short distance, without support at the 

 lower margins of the plates. Radials alternating horizontally with the 

 basals, pentagonal, with the angular face below, and much smaller than 

 the succeeding brachials. Anals in a single vertical series, interlocking 

 with adjacent brachials, and extending well up toward the arm bases. 

 Primibrachs two, increasing in width upward ; the first one sloped at 

 the lower corners and widening rapidly upward ; the axillary primibrach 

 followed by two to three bifurcations, giving six to eight arms to the ray, 

 or thirty to forty in all. The ray divisions are marked by a narrow, 

 longitudinal rid<j;e, originating at about the first bifurcation, becoming 

 more prominent upwards, and gradually passing into the free arms. The 

 last bifurcating plate in the brachial series gives out at one side a fixed 

 pinnule, incorporated in the calyx by lateral union with adjacent brachials, 

 puling out between the arm bases and becoming free. Two of such 

 pinnules abut at the outside of the rays; two also lie adjacent between 

 some pairs of arm bases within the ray, between some pairs one; and some- 

 times two arm series are in contact without any pinnule intervening. 

 Usually, but not uniformly, the pinnule is given off at the outside of the 

 dichotom. Arms slender, highly angular on the back, composed of cunei- 

 form plates narrowing alternately to a short face at the margin, the wider 

 end supporting a pinnule alternately at either side; by reason of the 

 thinness of the intervening plates at the margin the pinnules lie in close 

 proximity. 



