436 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



far as observed, of uniform size. To a length of about two inches the joints 

 are of equal length, and there are no iuternodal joints. But when the latter 

 make their appearance, they increase rapidly to seven to the internode, which 

 seems to have been the maximum number. The upper joints, and the nodal 

 ones below, are rounded at their edges, and project conspicuously beyond the 

 sides of the intervening ones. 



Horizon and LocaEly. — Keokuk limestone ; White's Creek Springs, near 

 Nashville, Tenn. ; Button Mould Knob, Ky. ; Keokuk, Iowa, and Warsaw 

 and Nauvoo, Ills. 



Types in the (Worthen) Illinois State collection, Springfield. 



Loboerinus Nashvillse var. subtractias (White). 

 Plate XXXI. Figs. 2a, b. 



1862. Aetinocrinus Naskvilla var. mhtmctus — Wuite ; Proceed. Bost. Soc. Nat. Hist., Vol. IX., p. 16. 

 1881. Batocriaus NashvUtce, var. subtradus — W. and Sp. ; Revision Palajocr., Part II., p. 167. 



This variety differs from the typical form in being less strongly lobed at 

 the arm regions, and in having no spines upon the anal tube. The plates of 

 the tube are but slightly convex, and each one is surmounted by a small 

 conical protuberance in the centre. It also differs in the structure of the 

 stem. In specimens from the Burlington limestone, and Burlington and 

 Keokuk Transition bed, the proximal stem joints are shorter than the suc- 

 ceeding ones, and all have an angular edge ; while in the specimens from 

 the Keokuk limestone proper the edge is rounded. At three inches from 

 the calj-x, all stem joints are nearly of uniform size. 



Ho'rison and Locality. — Upper part of Upper Burlington limestone and 

 Burlington and Keokuk Transition bed ; Des Moines Co., Iowa ; Henderson 

 Co., and Nauvoo, Ills. 



Remarks. — Dr. White gives the absence of the interdistichal piece as the 

 principal distinction between the two forms; this, however, is not a persistent 

 character. We have a number of specimens from the true Burhngton beds 

 in which that plate is represented in one or more rays. 



Loboerinus robusttis W. and Sp. (nov. spec). 

 Plate XXX. Figs. 8a, h. 

 A large species. Calyx about as high as wide, deeply and broadly de- 

 pressed between the rays. Dorsal cup but little higher than the ventral disk, 

 the sides slightly convex, constricted at the basi-radial sutures. Plates almost 

 flat and without ornamentation or other markings ; suture lines somewhat 

 srrooved. 



