804 THE PALEONTOLOGY OF MINNESOTA. 



[Oyrtoceras neleus. 



affinities of these species are with Oncoceras and Clinoceras. Some light is thrown 

 upon these facts by observations recently made upon the early stages of the shell 

 in the genus Bactrites* where it appears that in late Devonian represenatives of 

 this genus the swollen tube is a growth-stage immediately succeeding the pro- 

 toconch. It is hence a primitive condition, or at least it may be regarded as 

 indicating such a condition in such nautiloids as reveal it at any growth-stage. 

 We find that this inflation of the tube is a normal mature character in many early 

 Silurian genera, but is continued into the Devonian only in the genus Gomphoceras. 



CYRTOCERAS NELEUS Hall, 1861. 



PLATE LIX, FIGS. 17-20. 



Cyrtncerag neleum HALL, 1861. Kept. Supt. Geol. Surv. Wisconsin p. 40. 



Original description; "Shell of small or medium size, very gradually expanding 

 from the apex and strongly curved, transverse section circular or subcircular, very 

 obtusely subangular on the back in casts, most ventricose on the ventro-lateral 

 region. Septa closely but not evenly arranged, averaging about nine in a space 

 equal to the transverse diameter of the shell, curving forward to the dorsal sides, 

 their margins undulated especially toward the outer chamber where they become 

 crowded. On the ventral side the septa have a broad advancing curve. The 

 exposed surface of the septa shows the greatest concavity a little on the ventral 

 side of the center. Siphuncle dorsal, comparatively large. Surface marked by 

 transverse, slightly undulating annulations, which are strongly and abruptly curved 

 backwards on the dorsum. Diameter of the large specimens five-eighths of an inch," 

 To this species I have referred a number of specimens which conform to the 

 above description, though the surface markings in the specimens are not distinctly 

 annulations but rather strong concentric striae grouped in bundles and presenting 

 the appearance of low and obscure annulations. Some of this material is of good 

 quality, one specimen in particular retaining nearly the entire extent of the shell, 

 showing its slender and graceful form, and making a little less than one volution. 

 The broad, simple aperture (dorso-ventral diameter 18 mm., lateral diameter 

 21 mm.), rather shallow body-chamber (15 mm. on the dorsal surface) and the 

 numerous septa, which number forty in the entire length, serve to characterize it. 

 This specimen is an internal cant and along the venter the comparatively large 

 siphonal beads are clearly exposed. Other examples, in which there has been no 

 abrasion of the ventral surface, show the strong upward curvature of the septa and 



The writer In the American Geologist, vol. xlv, p. 37, 1894; "The Early Stunts of Itact rites ." 



