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310 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Horizon and Locality. — Upper Helderberg group \ Falls of the Ohio, 

 near Louisville, Ky. 



Tijjpc in the Ljon collection at JefFersonville, Ind. 



Remarks, — Actinocrinus multicornus Lyon is undoubtedly a mere varia- 

 tion of this species. The addition of sniall spinous extensions upon the first 

 costals and first interbrachials is not a sufficient reason for specific distinction. 



DOLATOCRINUS Lyon. 



1857. Lyon; Geol. Rep. Kentucky, Vol. HI, p. 482. 

 1877. S. A. Miller ; Cat. Amer. Palgeoz. Toss., p. 11. 



1881. W. and Sp. ; Revision Palseocr., Part II., p. 124 (Proceed. Acad. Nat. Sci. Plnla., p. 298). 

 Syn. Cacabocrinus — B.K-LL', 1862, 15th Rep. N. Y. State Cab. Nat. Hist., p. 137. 



Calyx depressed. Dorsal cup flattened below, sometimes to the full 

 height of the costals j the plates generally ornamented with radiating 

 ridges and nodes. Ventral disk but slightly elevated, surmounted by a 

 large, almost central tube; the interambulacral spaces depressed. Basals 

 anchylosed, the lines of union obliterated. Radials large and hexagonal. 

 Costals two; the first quadrangular, with convex upper and lower faces, 

 narrower than either radials or second costals, and wider than long; the 

 upper one pentangular. Distichals two to four in species with only two 

 primary arms ; but when there are additional bifurcations in the calyx there 

 is but one. Ambulacral openings large, arranged in groups, with wide 

 interspaces, and directed upwards. Arms biserial, generally bifurcating. 

 Interbrachials rather numerous, there being generally three ranges. The two 

 proximal rows consist of a single plate each, of which the first is the largest 

 plate of the calyx, rising to the top of the first distichals ; the upper row 

 connecting insensibly with the interambulacral ^Dlates. The latter plates 

 consist in most of the species of a single row of from five to seven rather 

 large cuneate pieces — the smaller end directed downward — which, except 

 the three middle ones, are not in contact laterally throughout their full 

 length, their lower ends being slightly excavated, so as to leave narrow slit- 

 like openings between the plates, two to three to each side of the interradius^ 

 or four to six to the whole area. Some species have two rows of interambu- t 



lacral plates instead of one, four to six smaller ones being placed beneath the ^ / 



others, and the upper margins of these plates are slightly pierced by the 

 lower ends of the slits. Above the interdistichal areas, there are rarelj^ more 

 than two slits, and not exceeding four. In the dorsal cup, the arrangement 







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