BATOCRINID &. . ABD 
Type of the genus: Dorycrinus mississippiensis Roemer. 
Ltemarks.— In the Revision, Part II., we referred to this genus Dorycri- 
nus canaliculatus and Actinocrinus (Celocrinus) concavus Meek and Worthen, 
Actinocrinus subaculeatus Hall, and A. parvus Shumard, all of which we have 
now arranged under a new genus Aorocrinus, along with Dorycrinus imma- 
turus, D. parvibasis, and D. radiatus, described by us in Vol. VIII. of the 
Geological Report 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 Rormer. 
Plate XLII. Fig. 1, and Plate XLIV. Figs. 2, 8. 
1854, Rormer; Archiv. f. Naturg. (Jahr. XIX.), Band I., p. 218, Plate 10. 
1862. Dusarpin and Hur; Hist. natur. des Zoophytes Echinod., p. 143, Plate 3, Figs. 1-3. 
1873. Mexrx and Worturn; Geol. Rep. Illinois, Vol. V., p. 380. 
1881. W. and Sp.; Revision Paleoer., Part II., p. 179 (Proceed. Acad. Nat. Sci. Phila. p. 353). 
Syn. <Actinocrinus (Dorycrinus) mississippiensis, var. spiniger Hau; Suppl. Geol. Rep. Iowa, 1859, 
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. Radials. once anda 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, those of the same ray equidistant, the spaces intervening between 
the rays twice as wide as those between their subdivisions, 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 
