110 



Report of the State Geologist. 



the facts with regard to the points raised: (a) The living chamber may cover 

 though rarely exceed an entire volution; this is also true of Torn, uniangu- 

 lare; (b) the growth lines are curved and indicate a pretty deep hyponomi- 

 sinus; (c) labial ridges are unknown; (d) the entire course of the suture at 

 maturity is shown in the adjoining figure, and it will be observed that its 

 internal course is undivided as in Tornoceras. Moreover, it will be clear that 

 its entire course corresponds with precision to an early sutural condition of 

 Tornoceras ivrdcmgulare. "We are thus compelled to infer that the features 

 cited can not be regarded as determinative of the genus Parodoceras. With 

 present evidence the most dependable basis of distinction in these genera is 

 the acceleration of Tornoceras over Parodoceras in sutural structure. 



Tornoceras is a genus whose suture is susceptible of considerable varia- 

 tion in the prominence and curvature of its lobes and saddles. This fact was 

 sufficiently, shown by the Sandbergers in their long list of variant expressions 

 of Tom. retrorsum and is again brought out with much force both by Kayser 

 and by Holzapfel (op. cit. pp. 82, 83). The latter especially observes that 

 in the older forms the ventral saddles are very inconspicuous, the lateral lobe 

 flat, while the lateral saddle is abruptly curved. This is the Parodoceras 

 condition which that author finds to be an ontogenic phase of Tornoceras, his 

 observations thus confirming those of others (Hyatt, Beecher and the writer) 

 and serving to establish the claim of Parodoceras to generic distinction. The 

 fundamental forms of Tornoceras from the middle Devonian illustrate a pro- 

 gressed condition in which the strength of lobes and saddles is intensified. 

 Among those forms of the genus where there is as yet no angulation of the 

 lateral lobes, all lobes and saddles retaining their rotundity, this increase in 

 curvature is progressive into the faunas of the upper Devonian. The evidence 

 from the European goniatitine faunas agrees with that we have to present, 

 but here we observe the continuation of Tornoceras into the fauna of the 

 Choteau limestone of Missouri, as recently made known by S. A. Miller and 

 W. F. E. Gurley * where it is represented by a strongly lobed species (Torn. 

 Jessie, M. and G.) approaching in its suture our form, Torn, rhys'u/m. 



Kayser, in his revision of the Sandrergkrs 1 determinations of Torn, 

 retrorsum, f pointed out the interesting fact that in the earliest and latest 

 forms of German faunas, the lateral lobes are acutely angled while in the 

 species of the middle and especially upper-middle Devonian, these lobes ;ive 

 round. This is finely exemplified in the lowest Devonian species. Torn. 

 inexpecUtium, Freeh, which, as observed by this author, is hardly to be distin- 



* Bull. No. 11 of the Illinois State Museum, p. 4G, pL v, figs. 18-20, 1896. 

 t See Kaysek. Zeltschr. der deutsch Red. Geselsch. vol C5. 



