BATOCEINID^. 489 



narrow and very long, curving abruptly from the basal concavity to the 

 upper edge of the dorsal cup, then tapering and lising somewhat bej'ond 

 the second interbrachials which lie at both sides of it : the latter formino' 

 extremely narrow strips, which rest against the curved up lateral faces of the 

 second distichals. Ventral disk sabpyramidal, the interradial spaces slightly 

 depressed ; plates highly convex, except the iuterambulacral pieces, which are 

 almost flat and considerably smaller. Surface of the plates finely granulose. 

 The posterior oral, which is as large as any two of the others, and slightly 

 excentric in position, is surrounded by eight plates : viz., the four smaller 

 orals, two large anal pieces, and two radial dome plates of almost the 

 same size as the orals. Near the periphery there is over each ray another 

 large radial plate, and over the posterior ray toward the anal side a second 

 smaller one, which is wanting in the rays with two arms. " The interam- 

 bulacrals consist of five to six pieces, and two other plates overlie the 

 ambulacra. Column comparatively narrow ; the nodal joints slightly wider, 

 ■with convex outer faces. 



Horizon and Locality. — Keokuk group ; White's creek, near Nashville, 

 Tenn., and Pilot Knob, near Louisville, Ky. 



Type in the Mineralogical Museum at Breslau. 



Remarks. — This species is remarkable for the extreme length of its first 

 interbrachial pieces, rising as they do to the top of the dorsal cup, and the 

 great tumidity of the anal area, which, together with the form of the calyx, 

 distinguishes it readily from the other species. 



In 1878 * we placed Agaricocrinus Inillatus Hall, A. excavatus Hall, and 

 A. nodosus Meek and Worthen as synonyms imder this species. Since then 

 we obtained a large number of additional specimens, especially from the 

 typical locality, which show that these forms can be specifically separated. 



Agaricocrinus Americanus, var. tuberosus (Hall) W. and Sp. 

 Plate XL. Fig. 6, and Plate XLII. Fig. 4. 



1850. Tkoost; List of Crin. Tenn. (Proceed. Am. Ass. Adv. Sci. Cambr. Meet., p. 60). 

 1850. Hall; Geol. Rep. Iowa, Yol. I., Part II., p. 617, Plate 16, Figs. 2a, b, c. . 



The specimens for which we propose this variety have been generally 

 regarded as synonymous with A. americamts. A comparison, however, of 



* Proceed. Acad. Nat. Sci. PliUa., p. 2i0. 

 62 



