Smith.] ^5-^ [Oct. 2, 



Class Cephalopoda. 



Order TetrahrancTdata. 



Suborder Nautiloidea. 



Genus Endolobus, Meek aud Worthen. E/ulolobus {Nautilus) vds- 

 souriensis Swallow, sp., PL xxi, Figs. 1-8. Nautilus missouriensis 

 Swallow, Trans. St. Louis Ac. Sc, 1857, p. 198. Endolobus missourien- 

 sis Swallow, sp., C. A. White, Indiana Geol, Survey, 1883, p. Ui6, 

 PI. XXXV, Figs. 1, 2. 



This species resembles very closely Endolobus spectabilis Meek and 

 Worthen, Geol. Siirv. Illinois, u, p. 308, PI. xxv, Fig. 18, and, as Dr. C. A. 

 White* remarks, almost the only reason for regarding them as distinct 

 species is their occurrence in such ditlerent horizons as the Chester Lime- 

 stone of the Subcarboniferous, and the Coal Measures. Also Dr. White's 

 specimen was i)oorly preserved, and he thought it might possibly have 

 had the nodes originally. It is really impossible to recognize the species 

 by Swallow's imperfect original description, but Dr. White's description 

 is very useful in determining this species, which in the Coal Measures 

 of Arkansas does not have nodes on the sides of the shell ; the difference 

 is all the more probable, because in the Fayetteville shale, Lower Car- 

 boniferous, of Independence county, near Mooretield, was found an 

 Eiidolobus, with very strongly marked nodes, resembling, if not identi- 

 cal with, E. spectabilis. 



This species also resembles Endolobus {SolenocJieilus) indianensis 

 Worthen, Geol. Surv. Illinois, viii, p. 150, PI. xxviii, Fig. 1, but on the 

 Arkansas specimens the whorls are more embracing, are broader and 

 not so high. 



In E. gibbosus Hyatt, Second An. Rept. Geol. Survey, of I'exas, p. 353, 

 the whorls are much more flattened, and the umbilicus is narrower, 

 and the umbilical shoulder subangular, while in E. missouriensis the 

 shoulders are round. In both, as in E. spectabilis, in adult specimens 

 the outer whorl embraces nearly one-half of the next inner whorl. The 

 septa are like those of E. spectabilis, and are far apart, genth' sinuous 

 and deeply concave. The internal lobe is deep and funnel-shaped. 

 The siphon is slightly nearer the internal than the external side, and is 

 slender. 



The casts are smooth, but some specimens have the shell parti}' pre- 

 served. It is ornamented Avith tine, sharp, spiral lines crossed by finer 

 lines of growtli, about one-half as far apart as the spiral lines, giving a 

 finely reticulated appearance to the shell ; these transverse lines bend 

 sharply backward on the outside of the whorl. 



In our collections are septate fragments of specimens that must luive 

 been at least four inches in diameter, and the body chamber would have 

 added about one-half of another revolution, so this species altaliied a 

 diameter of not less than six inches. 



* Geol. Surv. Indiana, 1883, p. 166. 



