Clarke — The Naples Fauna. 



63 



ornamentation, likewise, is extreme in its simplicity; simple varices are intro- 

 duced at the close of the smooth larval stages, and are continued in their 

 simplicity for a much longer period than in any other form, not exceeding 

 even Mantic. tardum. We find them throughout the extent of the third 

 w horl, and thereafter they seem to become obsolescent without modification. 

 As to septation, the adult whorls here, as in Mantiv. fazciatlatinn, Mantic. 

 tardum, etc, indicate a condition immature in the Intumescens type. 



Manticoceras apprimaturn occurs in the Styliola limestone' of Middlesex 

 and in the Naples beds of Naples; it has also been found near Griswolds, 

 Wyoming county. It is not of frequent occurrence. 



Manticoceras tardum, sp. nov. 



Plate I. Fig. 13; Plate VI, Fig. 31. 



The early whorls of this species are highly ornate and the elevated con- 

 centric stria?, commencing at the close of the smooth nepionic condition, come 

 in singly dining the early neanic stage, just as in ManUc. Pattersoni and 

 Mantic apprimaturn, but while these varices very soon thereafter become 

 increased by intercalation in Mantic. Pattersoni, they do not so multiply in 

 Mantic. tardum, but this primitive expression of single, simple, distant lamellae 

 extending fully about the whorl to the umbilicus, is maintained to the com- 

 pletion of the third volution very much as in Mantic. apprimaturn. During 

 the fourth volution subsidary striae are very gradually introduced, but these 

 are very faint and do not greatly obscure the general regular effect of the 

 ornament. Over this whorl the entire surface marking becomes more and 

 more faint. This peculiar character of the ornament is distinctly primitive 

 with reference to Mantic Pattersoni and Mantic faseiculatu m and essentially 

 parallel to it, somewhat in advance of Mantic. apprimaturn. Indeed we may 

 say that in respect to this feature only, these forms stand in the following pro- 

 gressive relation: Mantic. apprimaturn, Mantic. tardum, Mantic Pattersoni, 

 Mantic. fa scicu la turn. 



The umbilication of Mantic. tardum is much greater than that of Man- 

 tic. Pattersoni and Mantic. apprimaturn, while equaling that of Mantic. fasci- 

 eulatum. The form and cross-section of the whorl is distinct from both of 

 these at parallel growth-stages, being broader and flatter on the venter, but in 

 no case do the specimens indicate a ventral keel or hyponomic sinus. 



