en eA nce ap ne 
Se ss = - —— ss ee 
BATOCRINID&. ATT 
way between the large oral and the arm regions, and opens out laterally. 
Structure of arms and column not known. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa. 
Type in the (Worthen) Illinois State collection, Springfield. 
Remarks. — Closely approaching Aorocrinus parvibasis, which has a simi- 
lar base, and resembles it in its general outline; that species, however, has a 
very different arm formula, andthe plates of the calyx are distinctly convex. 
Aorocrinus parvus (Sxvm.). 
Plate XLV. Figs. 11a, b. 
1855. Actinocrinus parvus —SHUMARD; Rep. Geol. Surv. Missouri by Swallow, Part IT., p. 193, Plate 4, 
Fig. 9. : 
1881. Dorycrinus parvus —W. and Spr.; Revision Paleocr., Part II., p. 179 (Proceed. Acad. Nat. Sci. 
Phila., p. 353). 
Syn. Actinocrinus symmetricus —Hatt, 1858, Geol. Rep. Iowa, Vol. I., Part IT., p. 574, Plate 10, 
Figs. 8a, 6. 
Syn. Doryerinus amenus—S8. A. MittER; 1891, Geol. Surv. Missouri by Arthur Winslow, Bull. I, 
p. 35, Plate 4, Figs. 5 and 6. 
A small species. Calyx rotund; the dorsal: cup higher than the ventral 
disk, slightly obconical; the peripheral portions abruptly projecting outward, 
and distinctly lobed; the interspaces between the rays broadly and deeply 
excavated, and there are smaller excavations between their main divisions. 
Plates flat and without markings, except an obscure longitudinal ridge upon 
the costals and distichals. : 
Basals rather large, forming a broad, shallow cup with a narrow excava- 
tion at the bottom. Radials very large, almost as long as wide; the trun- 
cated upper faces as wide as the upper face. First costals quadrangular, 
once and a half as wide as long, the second quadrangular, smaller than the 
first. Distichals one or two. All divisions in which palmars are represented 
have but one distichal, but those in which they are wanting have two. The 
anterior ray invariably has but two arms, the two posterior ones from three 
to four, and the antero-lateral rays from two to four, frequently the left 
having more than the right, or vice versa. The number of fixed palmars 
varies from one to two, and large specimens generally have a small inter- 
distichal. Arm openings directed slightly upwards, and arranged in groups 
of two or one. Arms one from each ambulacral opening in the calyx; they 
are short, heavy, biserial; their plates moderately short, and every fourth 
piece extended into a well defined lateral spine. Interbrachials five to seven: 
