Clarke — The Naples Fauna. 



121 



ToRXOCERAS RHYSUM, sp. llOV. 

 Plate VIII, Fig. 14. 



This rare species is of small size, narrowly but distinctly umbilicated to 

 an ephebic growth stage, and the surface of the shell is characterized through- 

 out by its low, broad corrugations, curving retrally on the lateral slopes of the 

 whorl, making a very pronounced and acute forward bend ventro-laterallv and 

 thence at a sharp angle curving backward over a well 

 defined venter where their strength is so increased that they 

 present the aspect of a series of festoons. This unusual 



V 1 Figure 100. Tornoctrat 



ornament gives the species a very striking expression. The rh v ,um - The Rdult suture - 

 whorl section is somewhat less compressed than in normal forms of Torn, 

 vniangulare, and is distinctly more convex than in lorn, hicostatum. The 

 lobation of the suture is more sharply developed than in Torn uniangulare 

 and is very similar to that of Torn, bicostafavm. The magnosellarian saddles 

 are long and prominent, the ventral saddles and ventro-lateral lobes deep, sub- 

 equal and symmetrical ; the ventral lobe is deep and acute. 



Our material representing this species fails to give us further details of 

 its character and development phases. It has been found only in a single 

 calcareous concretion from the soft shales at Java village, AVyoming county, 

 associated with Gephyroceras aitaphraetum. The species is readily distin- 

 guished from the other forms of Tornoceras here described, by the character 

 of its ornamentation, and from Torn, hicostatum in particular, by the absence 

 of the sharply defined peripheral band. 



General Observations on Tornoceras. 



It has already been observed that, in defining the genera Parodoceras 

 and Tornoceras, Professor Hyatt regarded the latter as a probable derivative 

 of the former in the line of Anarcestes. 



As to this more remote origin of Tornoceras, there are some con- 

 siderations which need to be carefully weighed. The oldest species of 

 Tornoceras known in American faunas is the Torn. Mith/raas, Hall, from the 

 Corniferous limestone (upper lower-Devonian) ; a large, closely umbilicated 

 and, in respect to suture, fully developed form. Following this appear next 

 in order. Parod. discoideum, Torn, uniangulare and Torn. Ohioense, in the 

 faunas of the Hamilton group. In this country, also, Anarcestes is not 

 known before the opening of the middle Devonian and is represented by only 

 a single species, A. plebeiformis, Hall (very closely allied to A. lateseptatus y 



