HEXACRINUS. 189 



ECHINODERMATA, Klein, 1734. 



1. Class.— CRINOIDEA, Miller, 1821. 



1. Order.— CAMERATA, Wachsmuih and Springer, 1885. 



" Brachials, and often interbrachials, included to a varying extent in the dorsal 

 cup, and ambulacrals of the same included in the tegmen, all these plates being 

 immoveably united by close suture ; anal interradials usually distinct ; arms 

 pinnulate; no axial canal. " 



The above definition is given by Mr. F. A. Bather, to whose kind help in the 

 following pages I am very much indebted, and whose system of nomenclature I 

 have mainly followed. 



I. Family. — Hexacrinid2E, Wachsmuih and Springer, 1885. 



1. Genus. — Hexacrintjs, Austin, 1843. 



Dorsal cup conical or subglobose, sculptured or nodose, with bilateral 

 symmetry. Basals three, viz. one small in interradius and two large, though they 

 may approximate in size. Radials five, very large, excavate above. Primibrachs 

 of 1 to 4 rows, minute, not generally filling the excavation, which includes the first 

 axillary, which forms the base of two free arm-branches to each ray. Anal plate 

 narrower than the radials, in line with them, and supporting two or three plates. 

 Upper margins of adjacent radials usually supporting a pronounced interradial 

 plate of the tegmen. Tegmen somewhat raised, composed of polygonal tubercu- 

 lated plates. Anus subcentral or lateral, forming a simple opening, or supported 

 by a small tube composed of small polygonal pieces. Column cylindrical ; some 

 columnals larger, nodose or sculptured, all with radiated articular faces and a 

 small, circular, central canal. 



