Clarke — The Naples Fauna. 



69 



the venter itself there is a short projecting extension. Thus the curves of the 

 margin have almost no correspondence with growth lines on the body <>f the 

 whorl. 



We look upon this peculiarly conformed aperture, so unusual among the 

 goniatites and so often duplicated among the ammonites, as a distinctly em- 

 phasized gerontic character. There can be no doubt that in earlier and in 

 mature stages the aperture does conform in outline to the concentric growth 

 lines, and here likewise, up to within a very short distance from the aperture 

 itself, this conformity must have existed; but beyond this point, with the 

 actual completion of growth this remarkable departure is presented. That 

 this condition, involving the filling up of the hyponomic sinus and the com- 

 plete alteration of the lateral curves, had existed for but a brief period is 

 sufficiently shown by the fact that growth-lines actually concentric to the 

 aperture are most obscure and traceable only for a little way from the margin. 



These large specimens being from six, to six and one-half volutions, show 

 an increasing narrowing of the venter without tendency toward carination, 

 and abruptly sloping lateral surfaces. That they represent the shell, Mantle, 

 rhyndiostoma, is demonstrated by several specimens which have been dia- 

 metrically parted through the umbilicus and display the succession of fat 

 whorls characterizing this paraphrase. The sectional figure given on p. 68 

 (fig. 42) is taken from the same specimen as that figured in Plate V, the 

 inner whorls being retained in their fulness. 



Comparison of the aperture in this specimen with the fragment of the 

 carinate body-whorl of Maritic. oxy, in which a part of the apertural outline 

 is retained, will show distinct differences. The latter possessed broad lateral 

 ears, but these seem to have been rounded and not acute. They were, also, 

 situated considerably further up on the side of the whorl, and nearly corres- 

 pond with the curves of the concentric pilae. 



Manticoceras contractus, sp. nov. 



Plate VI, figs. 1, 2. 



In adult condition these shells are of relatively small size, very closely 

 umbilicated and the whorls have a longer and more convex lateral slope than 

 Mantic. Pattersoni. These features serve to distinguish the species without 

 closer scrutiny. 



The protoconch and nepionic stages are as in Mantic. Patterson). 

 Simple ornamental varices are then abruptly introduced over the whorls, but 



