Clarke — The Naples Fauna. 97 



essential modification, the suture showing a gradual increase in the strength 

 of the primitive lateral saddles and this increase is continued through and 

 beyond the period of the smooth conch, probably for one-half to three-fourths 

 of a volution. The formation of the hyponomic sulcus was contemporaneous 

 with the introduction of the other surface ornament. 



The nea ii ic stage. This is opened by the appearance of the simple, low, 

 elevated surface lines and the commencement of the hyponomic sulcus. 

 Dining its initiative stages the form of the whorl attains the outline charac- 

 terizing that of the mature normal Manticoceras, with the ventral flattening 

 superinduced upon it. Such a form is that presented by a species like Mantic. 

 carinatus Beyr. in which the intvmescens suture is associated with a ventral 

 keel, or like that afforded by late gerontic conditions of Mantic. Patterson /, 

 when the ventral ridge becomes best defined. 



The intumescem characters have not, however, developed pari passu and 

 are not presented simultaneously. That is to say, the neanic stage covers the 

 entire period in which the intvmescens traits are presented in respect to orna- 

 mentation, septation and whorl section, but at the precise time when anyone 

 of these is nearest its expression in the mature Mantic. Patterson /, the others 

 are not coincident. Thus the Pattersoni whorl section is here attained near 

 the beginning of the third volution. This is one-half volution after the intro- 



O ZD 



duction of the simple ornament and nearly a half volution before the 

 disappearance of the simple anarcestian suture, and the appearance of the 

 ventral saddle and ventrolateral lobe. The anephebic inl/wmescens suture 

 (that of Mantic. simulator with rounded lateral lobe), is well-defined only at 

 the end of the third volution. The umbilication is a feature in which there 

 is no agreement with Mantic. Pattersoni, except in the primary volution of 

 the shell in both. It is a character which gives a pronounced individuality to 

 the species from the neponic stage upward, and though passing through a 

 successive gain and loss, it is always of a different degree than that of 

 Mantic. Pattersoni. The neanic stage is clearly the period of assumption 

 of the Pattersoni characters, the Pattersoni growth-phase. 



The ephebic stage. Beginning with the fourth volution, the whorl 

 section becomes increasingly narrow and the venter flattened and deeply 

 concave. The normal suture with sharp lobes and saddles is well-established 

 in the course of the fourth volution, its later growth consisting of increase in 

 size and length. Ornamentation has become modified by the introduction of 

 fine intercalary striae. At the end of the fourth volution, umbilication has 

 7 



