BATOCRINID^. 455 



Type of the genus : Dori/crinus mississippiensis Roemer. 



Remarks. — In the Eevision, Part II., we referred to this genus Dorycri- 

 nus canaliculatus and Adinocrinus (Ccelocnnus) coneavus Meek and Worthen 

 Acdnocrmiis suhacukatus Hall, and A. parvus Shumard, all of which we have 

 now arranged under a new genus Aorocrimts, along witli Dorz/crinus imma- 

 turus, D. parviiasis, and D. radiatus, described by us in Vol. VIII. of the 

 Geological Eeport of Illinois. The arms of those species, instead of being 

 paired, are stouter and single, the first radial plates in the disk are not spini- 

 ferous, nor in any way distinct from the surrounding pieces, and their basals 

 are small and rounded at the lower margins. 



Dorycrinus mississippiensis Eoemee. 

 Plate XLIII. Fig. 1, and Plate XLIV. Figs. 2, 3. 



1854. Eoemer; Arcbiv. f. Naturg. (Jalir. XIX.), Band I., p. 313, Plate 10. 



1862. DnjAKDiu and Hcpe ; Hist, natur. des Zoophytes ^cliinod., p. 143, Plate 3, Pigs. 1-3. 



1873. Meek and Wortuen ; Geol. Rep. Illinois, Vol. V., p. 3S0. 



1881. W. and Sp. ; Revision PalsEOcr., Part II., p. 179 (Proceed. Acad. Nat. Sci. Pliila. p. 3.53). 



Syn. Actinocriiius {Dori/crinus) mississippiensis, var. spiniger Hall ; Suppl. Geol. Rep. Iowa, 1S59 

 p. 53. 



A large species. Calyx about as high as wide, asteriform in its ventral 

 aspect, deeply impressed and flattened at the posterior side, broadly truncate 

 at the lower end ; the ventral disk extended into six long, heavy spines ; the 

 plates from almost flat to strongly nodose ; suture lines more or less grooved. 



Basals large, forming a cup which is three times as wide as long, slightly 

 expanding to the lower margin, flat at the bottom, with a shallow depression 

 for the attachment of the column. Eadials once and a half to twice as wide 

 as long, the upper face concave. First costals comparatively large, wider 

 than long, quadrangular. Second costals a little larger than the first ; those 

 of the posterior rays generally hexangular, the others heptangular. Dis- 

 tichals one to each ray division, all of them axillary ; they are as large as 

 the second costals, and give off from each of their sloping sides a single 

 palmar, which supports two arms. Arm openings twenty, arranged in 

 groups, thoe of the same ray equidistant, the spaces intervening between 

 the rays twice as wide as those between their subdivision,?, and that of the 

 anal side about four times as wide. Arm structure unknown. First inter- 

 brachial large, generally as wide as high ; it supports two somewhat smaller 

 plates, which abut against the upper costals and the distichals, and these 

 are followed by two still smaller pieces, which are on a level with the 



