ACTINOCRINID &. 595 
depressed, and the dorsal cup more elongate proportionally. This is also the 
case with the specimens from the Lower Burlington bed, the calyx being one 
fourth higher than wide, and the specimens have but six arms to the ray, 
but are in other respects identical with those from the Upper bed. 
Physetocrinus dilatatus (M. and W.). 
Plate LXIV. Figs. 9, 10. 
1869. Strotocrinus (Physetocrinus) ig aloe ail Wortuen; Proceed. Acad. Nat. Sci. Phila., 
p. 162. Also 1873, Geol. Rep. Illinois, Vol. V., p. 368, Plate 10, Fig. 6. 
1881. Physetocrinus dilatatus —W. and Sp.; Revision Paleocr., Part IL., p. 157. 
Calyx moderately large, the cup saucer-shaped, rapidly expanding from 
the basals to the top of the distichals, and more rapidly thence to the free 
arms, which at their bases are directed almost vertically, and owing to their 
large size are much crowded. Plates of the dorsal cup slightly convex, with 
shallow indentations at the angles of the plates. 
Basals short, not thickened or expanded below; axial canal large. Radials 
and costals nearly of uniform size, a very little wider than long. ' Distichals 
almost as large as the costals, and of similar form; they support an arm, 
which is free beyond the second plate, and a palmar, which either supports 
two arms, or a single arm and an axillary post-palmar. The arms thus 
vary from six to eight to the ray; they are very stout, increasing in thick- 
ness from their bases up until their size is almost doubled at about two 
inches from the calyx. Regular interbrachials: 1, 2, 2,2, 2,1. Anal plate 
a little shorter than the radials ; followed by 2, 3, 3, 4 and two plates. In- 
terdistichals two to three. Ventral disk low-hemispherical, slightly plicated 
around the margin ; the plates small, irregularly arranged, and of about the 
same size. Anus excentric, at the top of a small protuberance. 
Horizon and Locality.— Upper Burlington limestone ; Burlington, Towa. 
Type in the Museum of Comparative Zodlogy. 
remarks. — This species is readily distinguished by the flatness of its 
calyx and its stout arms. 
