486 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



We have not seen the type specimens, and neither Miller's figures nor his 

 description enable us to make a satisfactory comparison. If it should prove 

 to be the type of a new genus, the projDosed name Cylicocrinus cannot be 

 used for that form, as it was preoccupied in 1855 by Joh. Miiller for a 

 Devonian genus. Miiller made the name " Culicocrinus," which has the same 

 derivation as Cylicociinus. 



AGARICOCRINUS (Tkoost) Hall. 



1850. Tkoost ; List. Crin. Tenu. (Proceed. Amer. Ass. Adv. Sci.), p. 60. 



1858. Hall (Subgenus of Actimcrinus) ; Geol. Rep. Iowa, Vol. I, Part II., p. 560. 



1861. Hall (Subgenus of Aniphoracrinus) ; Boslon Joum. Nat. Hist., Yol. TIL, p. 280. 



1866. Meek and Worthen (Subgenus of Actinocriims) ; Geol. Rep. Illinois, Vol. II., p. 210. 



1873. Meek and Woethen (Subgenus of Amphoracriims) ; ibid.. Vol. V., p. 499. 



1879. ZiTTEL (Subgenus of Amphoramnus) ; Handb. der Palffiont., Vol. I., p. 371. 



1881. W. and Sp. ; Revision Pateocr., Part II., p. 109 (Proceed. Acad. Nat. Sci. Pliila., p. 283). 



Calyx conical or depressed globose ; the lower face concave, flat or 

 broadly convex. Basals three, small, arranged horizontallj', and forming 

 a hexagon, which is partly covered by the column. Eadials rather small. 

 First costals quadrangular, rarely hexangular; the second pentangular or 

 hexangular according to the height of the interbrachials. Size of the second 

 costals and first distichals extremely variable, sometimes the former being the 

 largest plates of the calyx, and sometimes the latter. Arms two to four to the 

 ray ; the arm facets of the same ray contiguous, but each arm having a sep- 

 arate ambnlacral opening; the arm bases of adjoining rays separated by 

 interbrachials. The earlier species have two arms to the ray, but most of the 

 later ones three — some of them four — in the posterior rays, and two in the 

 others. When there are but two arms, the first distichals are followed by 

 a moderately short, somewhat cuneate second plate, which bends inward 

 like an arm plate, and this again by two rows of short, heavy arm plates, of 

 which the proximal one, and frequently those of the two succeeding rows, 

 are in contact with their fellows of adjoining arms. The arm plates inter- 

 lock with those of the opposite row, and the inner ones with the proximal 

 distichals, which are also alternately arranged among themselves. Arms 

 long and ponderous, heaviest at their bases, whence they taper gradually to 

 the tips. Interbrachials three or more ; in size as variable as the costals and 

 distichals, but all of them narrow and long. In some species the first plate 

 rises almost to a level with the arm bases, in others only to the middle of 

 the first costals, and in this case the two plates of the second range are 



