ACTINOCRINro^. 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. Strotocrimts {Physetocrinus) dilatatus — Meek and Wokthen ; Proceed. Acad. Nat. Sci. Pliila., 



p. 163. Also 1873, Geol. Rep. Illinois, Vol. V., p. 363, Plate 10, Fig. 6. 

 1881. Phi/setocrimis dilatatus — W. and Sp. ; Revision Palceocr., Part II., 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 lai'ge. 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 Loealiiy. ■ — Upper Burlington limestone ; Burlington, Iowa. 



Tt/pe in the Museum of Comparative Zoology. 



BemarJcs. — This species is readily distinguished by the flatness of its 

 calyx and its stout arms. 



