﻿575 



was the first to state that most of our Western forms of Heteroceras 

 probably had similar irregularities in the development of the last 



volution. 



Emperoceras* n. g. 



The young are hamites-like, so far as known in the neanic stage 

 and become helicoceran in the ephebic stage. It is not positively 

 known that they have an extended gerontic stage. 



Emperoceras Beecheri. 



Loc, Near Buffalo Gap, S. Dakota. 



This species has, in the earliest substage, observed probably the 

 metaneanic straight volution with straight costae, having each two 

 minute tubercles on the venter, and no intermediate untuberculated 

 and single costae. The section is compressed oval, the dorsum 

 broader than the venter. The siphuncle is certainly in the mesal 

 plane between the rows of ventral tubercles in this substage. The 

 sutures are simple and appear to be symmetrical, or more nearly so 

 than in the succeeding substages. 



The paraneanic is introduced when the hamites-like first bend of 

 this specimen is made, and is terminated by a permanent constric- 

 tion in the elbow of the second bend in both specimens of this 

 species. Bifurcated costae appear and intermediate untuberculated 

 costae in this substage. 



The next arm, probably the anephebic substage, is bent more or 

 less downwards, but the curvature is distinct from that of the met- 

 ephebic stage, and the form of volution in section is still a depressed 

 oval, although much more gibbous on the upper than on the lower 

 side. The section is that of a compressed ellipse, the ventrodorsal 

 diameters increasing faster than the transverse. 



The intermediate single costae running uninterruptedly across the 

 venter are more numerous in this substage, occurring from one to 

 three between each bifurcated and tuberculated costation. The 

 bifurcations are not always well marked, but they are more distinct 

 than those given in the drawings, and here and there a costation 

 may be single and have tubercles. This volution begins to twist in 

 the metephebic substage, and the asymmetrical helicoceran form is 

 fully developed in the flattening of the lower side and the increas- 

 ing gibbosity of the upper side, whether this be right or left, and 

 the tubercles are correspondingly deflected. The siphuncle has 



*" £ ) 'J.nrj po<? } deformed. 



