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shifted less, and consequently the upper row of tubercles is brought 

 over the trace made by this organ in the cast of the interior. 

 Great irregularity appears in this substage, the costse may be bifur- 

 cated at the tubercles and between them, or they may run across 

 the venter and be bifurcated at the base of the tubercle of the oppo- 

 site side. This ornamentation is similar to the fragment figured by 

 Gabb in Paleontology of California as Ammonites Cooperi, Vol. i, 

 PI. xiv. 



The dorsal crests formed by costae occupy the somewhat flattened 

 dorsum of the early part of the paraneanic substage, but when the 

 twisting begins these dorsal crests begin to be unsymmetrical also. 

 In other words, the lines of growth and costse assume the usual 

 direction and aspect of turbinate shells, whether Gasteropoda or 

 Cephalopoda. 



The spiral is quite irregular in the anephebic substage, but is 

 more regular in the metephebic and parephebic substages. In the 

 parephebic substage the tubercles disappear in this specimen. 



There is a decided contraction of the transverse diameter of the 

 spiral in this substage. 



The absence of the tubercles on this substage is similar to the 

 change that takes place in Nostoceras nebrascense at the same age 

 and enables one to classify all the substages satisfactorily. 



Pxiteloeeras,* n. g. 



After a careful survey of the forms referred to this genus, it 

 has become evident that there is a series having the following char- 

 acteristics and quite separable from the full-grown stages of any 

 other genus referred to the Nostoceratidae. They are, however, 

 not so easily separated from the young of Nostoceras if my obser- 

 vations are correct, since the single costae with two lines of tuber- 

 cles are found in the young of that genus and of Emperoceras. 

 This, however, is entirely in accord with the system advocated in 

 this and other publications and is in my opinion another argument 

 in favor of distinguishing the group by another name. 



The series of forms figured by Meek in his Invertebrate Paleon- 

 tology, PI. xxi, have a single costae with two rows of tubercles, each 

 costation being tuberculated. The ephebic stage is helicoceran 

 and the gerontic stage probably has the retroversal living chamber.. 



* , Ectrr / ?>os, becoming extinct. 



