44 Report of the State Geologist. 



lxix, figs. 1, 2). The specimen represents a nearly entire, rather small though 

 probably essentially adult shell with a characteristically broad venter, gradually 

 rounding sides, but it is without such elevated dorsal margin and abrupt dorsal 

 slope as there represented. It is important to indicate this, as the figure cited 

 presents an aspect actually characterizing, in this conspicuous elevation of 

 the dorsal margin, certain local expressions of Mantle, intumescens. The shell 

 is re-figured on our Plate I, fig. 14. Manticoceras simulator, with its rounded 

 lateral lobe is such a shell as the Gon. carinatus (not Beykich) of Sandberoer 

 and of Tschernysciiew, and while we are in ignorance of the surface character 

 of its shell we may also bring into comparison the Gon. lamellosus, Sandb. 

 and (ran. lamed, Sandb. var complanatus (Beyr.) Sandb. 



The probability has, at various times, been suggested that such shells are either 

 actual young of Gun. intumescens or stand as species in a phylonepionie posi- 

 tion with reference to the ephebic normal of intumescens, for we shall presently 

 observe that the acuteness of the lateral lobe in intwmescens is an adult condi- 

 tion (Hyatt, Holzapfel) and Mantic. simulator itself shows an increasing 

 sharpness in this lobe on successive septa over the last half of the final whorl. 

 But in the normal form of Mantic. intumescens- Pattersoni, the lateral lobe has 

 lost its roundness and become acute long before so great a size as that of 

 Mantic simulator is attained, and thus this species stands in a definite relation 

 to the former, that of retarded to complete development. In the present dis- 

 cussion we regard this form as one of several abnormals of Mantic. Pattersoni, 

 and as it is at least impossible to conceive a generic difference between its 

 known structure and that of Mantic. Pattersoni, we apply the term Manti- 

 coceras to the intumescens-group, and hold that Gon. intumescens must be 

 regarded as its typical species. Similar usage has been followed by Holzapfel, 

 v. Zittel and Tsciiernyschew. 



We must not, however, overlook the fact that Hyatt also introduced a 

 generic term, Gepiiyrocekas, specifying as its type-species the Gon. sinuosus, 

 Hall, as illustrated on plate lxx (figs. 73-75) of Palaeontology of New York, 

 vol. v, pt. 2. This is an Intumescens-zone fossil which we hold to be specific- 

 ally the same as Gon. Pattersoni. The specimens cited by Hyatt, and all of 

 the material which served for the illustration and description of the fossil are 

 casts of macerated shells such as occur commonly in the shales and slabby 

 sandstones of the Naples beds where, by wear before fossil ization and modi- 

 fications during and since that process, apparent umbilication has been greatly 

 increased and angularity of the suture much diminished. A strictly precise 

 construction of this generic term, therefore, leaves Gon. Pattersoni its type, 



