64 BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Formation and locality. — Keokuk horizon of the Tullahoma forma- 

 tion. White's Creek Springs, Davidson County, Tennessee. The 

 species is also recorded from Hardin County, Kentucky, and Craw- 

 fords ville, Indiana. 



Cat. No. 39896, U.S.N.M. 



BATOCRINUS GIBBOSUS (Troost). 



Plate L5, fig. 9. 



Actinocrinites gibbosus Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, 



p. 60 (nomcn nudum). 

 Actinocrinw gibbosus Shumard, Trans. Acad. Sci. St. Louis, II, No. 2, 1866, 



p. 344 (catalogue name). — Wachsmuth and Springer, Rev. Paheocrinoidea, 



II, 1881, p. 224 (catalogue name). — Miller, North Amer. Geol. and Pal., 



1889, p. 218 (catalogue name). 



The original description by Troost is as follows: 



This species has much analogy with the A. cornutus [Erelmocrinus praegravis] but it 

 differs from it in its form and the proportions of the different parts, the cup being in 

 proportion more elevated and the coronal integument more flat — the proboscis less 

 capacious, and showing the places of insertion of the fingers to the number of twenty 

 [eighteen]. The tubercles, particularly upon the coronal integument, are less elevated 

 and not so acute. 



The specimen here represented, the only entire one that I have found, is wholly 

 covered by a chalcedonic matter through which rise the tops of the plates, which are 

 elevated. There is no doubt that the size of the body was thereby increased and its 

 form, at least of the lower part, has been more or less changed, because the plates are 

 now further separated laterally from one another than they were in the live state. 



As the top of the plates are not covered, this siliceous exudation must have proceeded 

 from the interior of the body, through the joints of the plates which has extended these 

 joints. This fact I have observed in several of our fossils, and never on those that I 

 received from Europe; I have even found some that were entirely covered by similar 

 chalcedonic matter. The specimen now under consideration is totally siliceous but 

 the projecting plates are flinty while the substance that fills up the space between the 

 plates is chalcedonic. 



Supplementary description.— Although the plates of this specimen 

 have been widely separated by siliceous enlargement as described by 

 Doctor Troost, they are well preserved and their form and arrange- 

 ment can be determined. 



As indicated by a careful measurement of the plates, the height of 

 the calyx to the arm bases must have been about 35 mm., and the 

 tegmen probably about half that height. 



Basals large, bearing transverse nodes on which the crinoid would 

 rest if deprived of its stem. Sutures strongly beveled. Radials 

 large, wider than long. Plates of the radial series bearing transverse 

 sharp ridges which extend nearly the whole width of the plates. 

 Arm formula as follows: 1-2 ... 1-2 .. . 2-2 . . A . . 2-2 . . . 

 2-2, giving eighteen arms to the species. 



There is but one large interbraehial. which bears a rounded instead 

 of a transverse node. The first anal plate also bears a rounded node, 



