Clarke — The Naples Fauna. 



77 



MaNTK OCKRAS ACCELEKAWS, s(). nOV. 

 Plate VI, Fig. 10. 



A tachygenic phase of Mantic. inturnescens is presented by this small 

 shell which is, perhaps, in its normal condition, somewhat less umbilicated 

 than that species. At a growth stage where the diameter of the shell is 

 22 mm. the suture has attained the curvature characteristic 

 of the adult i/iftn/iesre/ix, but the septa are very closely crowded 

 and are nearly parallel, so that the interval between them is of 

 about the same width throughout their extent, a feature strikingly Figure no. Mant>: 



... coceras accelerans. 



different from the condition in Mantic. Pattersoni where the The sutures in 



, natural size and po- 



mterval between successive saddles is w-reat and between sue- sition. 

 eessive lobes small. In the last half-volution there are nineteen of these closely 

 appressed septa. This is a rare form of which we have seen but two 

 specimens, both from the soft Portage shales at Naples, X. Y. 



Manticoceras oxv, sp. nov. 



Plate II, Figs. 5, 6 ; Plate III, Figs. 1-3. 



This name is applied to a shell which may be regarded as in all respects, 

 an ultimate expression of Jf<r/ifi<: JPattersorii. It is of large, indeed of 

 gigantic size, its final whorls are sharply carinated and its septal sutures show- 

 extreme development of all curves. Itsgerontic expression in these particulars 

 is fortified by its late appearance in the fauna. Specimens are not known in 

 the lower beds of the Portage group and the species first appears not far 

 below the horizon of the Portage sandstones, sometimes in soft sandy shales, 

 sometimes in the flagstones, and again above the horizon of those sandstones 

 in what have been termed the Wiscoy beds of the Portage group. Such a 

 shell as this was included by the Saxdbergkrs and F. Roemer within the 

 limits of Mantic. inturnescens* 



We have represented on our Plate II a nearly entire individual <>f this 

 species, though of small size in comparison w ith other specimens found. This 



* Sandberukrs, op. cit. pi. vii, fig. 1 a, b; Roemer, Lethaea palaeozoiea, pi. 35, fig. 10. Roemer's figure has been 

 reproduced in such works as Koken's Die Vorwelt and Steinmann and Doederlein's Elemente der Paleontologie, as 

 exemplifying this species, though, as we have already explained, Beyrich's original was a shell without carination. 



In this connexion attention may be directed to the interesting shell identified by d'Archiac and ue Ver.neiil with the 

 Gon. Hceuinghausi, v. Buch. We have elsewhere observed that v. Bich's species is synonymous with Mantic. inturnescens. 

 That figured by the French authors (Descr. Foss. Rhen. Prov., pi. xxv, figs. 7 a. b.) is a quite distinct species. It is a large, 

 sharply carinate shell, with an accessory saddle which, Holzapfel observes, must exclude it from the genus Manticoceras 

 (Das Obere Mitteldevon ini Rliein. fiebirge. 1805. p. 117). Notwithstanding the fact that it is an upper middle Devonian 

 shell, both its form and its suture evince its great acceleration. Morphologically it is an important link between Manti- 

 coceras and Beloceras (Holzapfel), but Its time relations to the former genus indicate that we have still much to learn 

 of the earlier history of Manticoceras. 



