600 THE .CEINOIDEA CAMEEATA OF NOKTH AMERICA. 



CACTOCRINUS W and Sp. (nov. gen.). 

 (KaKTos a thorny plant, xpCvov a lily.) 



Calyx generally longer than wide, the ventral disk high, conical, passing 

 gradually into a strong, almost central tnbe. The plates of the cnp orna- 

 mented by radiating ridges and nodes. Basals three, comparatively short. 

 Costals two, generally hexagonal and heptagonal. Distichals 1 X 10, all 

 axillary. The succeeding orders of brachials, when present, also consist of a 

 single row of plates, but only one plate at each side of the ray is axillary ; 

 the other one is truncated, and gives off an arm which is free from the sec- 

 ond or third plate ; the axillary supports either two simple arms, or one from 

 one side and two from the other, the arms being given off alternately from 

 opposite sides like the pinnules. Arms equidistant or nearly so, long, bise- 

 rial and infolding ; back and sides generally covered with nodes or thorns, 

 and the pinnules with sharply pointed hooks. The pinnules are in close con- 

 tact, and those of one side of the arm are placed with their ventral faces 

 fronting those from the opposite side. They are composed of numerous 

 elongate joints, which, with the exception of the three or four distal ones, 

 are produced into sharp, prominent hooks, directed obliquely upward and 

 outward, and arranged in rows parallel to the sides of the arms. The hooks 

 of one pinnule curve over the back of the adjoining one, so as to give to the 

 mass of pinnules, in their dorsal aspect, the appearance of a fine network 

 in which their outlines cannot be distinojuished. The ventral furrow is cov- 

 ered by two rows of side pieces, which enclose two rows of minute covering 

 plates. Interbrachials numerous, separated from the interarabulacrals by the 

 upper row of fixed brachials, which are in contact laterally. The plates of 

 the ventral disk are more or less spinous, and so irregular in their arrange- 

 ment that it is often difficult to identify the orals and radial dome plates. 

 Anal tube very long and almost central Column large ; the axial canal 

 pentangular. 



Tt/pe of the genus : Oaetocrinus j^roboscidalis (Hall). 



Distribution. — Restricted in America to the age of the Kinderhook group 

 and Lower Burlington limestone, with a single aberrant survivor in the 

 Upper Burlington beds. The genus may possibly be represented in Europe 

 in the Mountain limestone of Ireland ; but, so far as we know, not in Bel- 

 gium, nor in the Yorkshire beds of England. 



