BATOCRINID&A. 427 
Dizygocrinus biturbinatus (Hatz). 
Plate XX XII, Fig. 9. 
1858. Actinocrinus biturbinatus — Hat; Geol. Rep. Iowa, Vol. I, Part II., p. 616, Plate 16, Figs. 5 and 
18738. tpdies Pipe — Mezx and Wortnen; Geol. Rep. Illinois, Vol. V., p. 367. 
1881. Batocrinus biturbinatus —W. and Sr.; Revision Paleocr., Part II., p. 165. 
Syn. Batocrinus lyonanus MittuR and Guriny, 1894; Geol. Surv. Llinois, Bull. 3, p. 18, Plate 3, 
Figs. 4 and 5. 
Calyx biturbinate, about as wide as high, the ventral disk as high as the 
dorsal cup. Plates below the arm regions flat, above slightly convex, their 
surface perfectly smooth; suture lines indistinct. 
Basals small, forming a hexangular, shallow basin, with a slightly pro- 
jecting rim at their lower margins. Radials once and a half as wide as long, 
the upper face straight. First costals quadrangular, considerably narrower 
and shorter than the radials; the second a little longer than the first and 
pentangular, their sloping upper faces at right angles. Distichals three in 
the anterior ray, two only in the antero-lateral ones. In the posterior rays, 
the divisions next to the anal interradius have two distichals, the others 
three. All divisions with two distichals are followed by 2 X 2 palmars, those 
having three directly by free arm plates. Arms sixteen (exceptionally seven- 
teen, there being sometimes an additional one in the anterior ray); simple, 
slender, pointed at their ends, and incurving; they are biserial from the 
second free plate, and provided with slender, long-jointed pinnules, Inter- 
radial spaces slightly depressed at the arm regions. Regular interbrachials 
three to four; the first very large, as wide as high. The anal interradius 
contains from seven to nine pieces, the anal plate being succeeded by three 
plates, and these by three and two; occasionally there is another small plate 
above, separating the palmars, and a similar plate sometimes occurs at the 
other sides. Ventral disk subconical, and extended into a central anal tube. 
The plates are but slightly convex and of almost uniform size, except that 
the posterior oral is twice as large as any of the four others. Column 
decidedly tapering; the joints nearest the calyx nearly twice as wide as 
those two inches farther down, the former with convex edges, the others 
almost cylindrical, and there are six joints to the last internode that is pre- 
served in the specimen. 
Horizon and Locality. — Keokuk group, near Keokuk, Iowa. 
Types in the (Worthen) Illinois State collection, Springfield. 
