490 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



authentic specimens froni White's creek near Nashville, Tenn., Eoemer's 

 typical locality, with those from Iowa and Illinois, which Hall described 

 and figured as Agaricocrinus tuberosus, shows that the latter are sufficiently 

 distinct to be recognized at least as a variety. The two forms resemble each 

 other in their general outlines, but the lower face of the calyx in the Iowa 

 specimens is considerably more concave ; their first interbrachials shorter 

 and not visible in a side view, or but very slightly ; the plates of the dorsal 

 cup are somewhat more convex, and the anal area is less tumid, and not so 

 abruptly protruding as in the typical form of A. americanus. 



Horizon and Locality. — Keokuk group, Keokuk, Iowa, and at Hamilton, 

 Nauvoo, and Niota, Ills. 



Ti/j^es in the collection of Wachsmuth and Springer. 



Agaricocrinus Wortheni Hall. 

 Plate XXXIX. Ficj. 9, and Plate XL. Figs. 5a, h, c, d. 



1858. Hall; Geol. Rep. Iowa, Vol. I., Part II., p. 619, Plate 16, Fig. 1. 



1881. W. aad Sp. ; Revision Pala;ocr., Part II., p. 113 (Proceed. Acad. Nat. Soi. Pliila., p. 287)- 



A large species. Calyx depressed pyramidal, pentagonal as seen from 

 above or below, the anal side broadly and deeply excavated, and the posterior 

 rays distinctly lobed. The plates of the dorsal cup to the middle of the 

 second costals placed within a deep concavity, which contains not only the 

 basals, radials and first costals, but the whole of the first interbrachials and 

 parts of the second. All succeeding plates of the dorsal cup are stretched 

 out almost horizontally, and only the arm facets and the third row of inter- 

 brachials are visible in a side view. The plates within the concavity are 

 perfectly flat ; while all radial plates from the second costals up are more or 

 less convex. 



Basals slightly projecting beyond the column. Radials nearly as long as 

 wide. The first costals fully as large, or even larger than the radials ; hex- 

 agonal, their upper angles truncated by the second interbrachials. Second 

 costals about twice as large as the first ; wider, but not as long. First dis- 

 tichals almost as large as the upper costals, their width much greater. The 

 second distichals, when represented, are wider than the first, but half their 

 length. The posterior rays, which have three or four arms, have but one 

 distichal in one or both divisions, which supports on each side a rather large 

 palmar, and this, which is formed like an axillary, is followed by the two 

 rows of arm plates. Arms twelve to fourteen, long, stout, tapering ; com- 



