BATOCRINID^. 477 



way between the large oral and the arm regions, and opens ont laterally. 

 Structure of arms and column not known. 



Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa. 



Type in the (Worthen) Illinois State collection, Springfield. 



Hemarks. — Closely approaching Aorocrinus parvihasis, which has a simi- 

 lar base, and resembles it in its general outline ; that species, however, has a 

 ■very different arm formula, and the plates of the calyx are distinctly convex. 



Aorocrinus parvus (Shum.). 

 Plate XL V. Figs. 11a, I. 



1855 . Actiiiocriiius parvus — Shujiard ; Eep. Geol. Surv. Missouri by Swallow, Part II., p. 193, Plate A, 



Fig. 9. 

 18S1. Doryerinus parvus — W. and Sp. ; Revision Paleeocr., Part 11., p. 179 (Proceed. Acad. Nat. Sci. 

 PbUa,, p. 353). 

 Syn. Jclimcriiius si/mmelricus — Hall, 1858, Geol Hep. Iowa, Yol. I., Part II., p. 574, Plate 10, 



Figs. 8a, b. 

 Syn. Dorycriims amanus — S. A. Miller; 1891, Geol. Surv. Missouri by Arthur Winslow, BuU. I., 

 p. 35, Plate 4, Pigs. 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 marking.s, 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. Eadials 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: 



