Clarke — The Naples Fauna. 



79 



its characters to show that we have here to do with an especially interesting 

 form. The specimen is of rather small size, the final whorl shown being 

 relatively broad and sloping in convex curves to a sharp, though 

 not keeled ventral edge. This whorl is septiferous and is evidently 

 one of the inner whorls of a somewhat larger shell, and we have 

 had no other instance of this carination, potentially gerontic in 

 Mardie. Pattersowi, parephebie in Mantle oxy, doubtless metephebic 

 in Mantic. (?) Hoeninghausi and Mcmtic. carinatum, here distinctly 

 developed at the beginning of epheby. The sutures are normal 

 but crowded, as shown in the accompanying figure, and the surface 

 of the whorl shows concentric rugae. 



This specimen was found in a loose block of sandstone among 

 the Portage outcrops in the town of Naples, and is associated with 

 numerous examples of Productella speciosa, Leptostrophia mno'onata and 

 Amhoccelia vmbonata. It has evidently been derived from a concealed layer 

 in or even above the upper sandstones, the species themselves indicating an 

 incursive association from the eastward fauna. 



Figure 62. 

 Man t icoct- 

 ras vag an s 

 sections of 

 early ephebic 

 whorls ; nat. 

 size. 



RECAPITULATION. 



The Paraphases of Manticoceras. 



We have here endeavored to emphasize the significance in the ontogeny 

 of this genus, of what have been usually regarded as differentials of minor 

 value. The ornamentation, its mode of introduction and modifications in 

 growth can now be properly estimated in determining the genetic position 

 of its species. In this generic group it is not to be considered of inferior sig- 

 nificance to the phases < >f septation itself. The conch was less quickly responsive 

 to organic influences and hence the whorl section maintains a uniformity in its 

 changes which makes it one of the most dependable characters of the genus; 

 notwithstanding, its phases serve to indicate very definite values in growth 

 and decline. Umbilication is a feature whose significance is often less easy to 

 gage, but whose value we have pretty clearly defined in our standard of com- 

 parison Mantic. Pattersoni. As to the embryonic (protoconch) and nepionic 

 stages, they prove to be invariable in all species here studied ; only with the 

 close of the nepionic phase do external differentials clearly manifest them- 

 selves. Such diverse expressions of the genus can not be properly estimated 

 without consideration of the local conditions with which they are involved. 



