﻿5±2 



this class. At any rate the ornamentation, form and lateral flutes 

 all plainly point to the same genetic stock as Koninickioceras, 

 whereas in Coelogasteroceras* there are no lateral flutes or faces and 

 a very distinct and more primitive shell, especially in the nepionic 

 stage, as may be seen in the section, Fig. 33 of PI. x. 



The figures of Coloceras globatum on PL x give the history of 

 the dorsal furrow. They show also that considerable variation 

 exists in the form of the ananepionic substage and it may be that 

 Figs. 10-12 belong to a different species from those that show a 

 flatter and more trigonal outline in the early stages. The umbilical 

 perforation, however, remains about the same in all the specimens. 

 This is of good size and there is no abrupt curve at the beginning 

 of the paranepionic substage which would account for the genesis 

 of the nepionic furrow in the dorsum of the specimen in Figs. 

 10-12, which is perfect in its proportions and markings. In the 

 specimens given, 1 and 2 and 7, there is a more abrupt curve 

 at this point and more sudden appearance of this zone, but the pas- 

 sage of the form into the nephritic outline is gradual even in these 

 specimens. The first suture in Fig. 10 obviously belongs to the 

 first living chamber of the metanepionic substage, while the second 

 and third are paranepionic, although the second is still within the 

 limits of the metanepionic volution, i. e. t built in that part before 

 the dorsal furrow appeared. The third suture is indented by the 

 furrow. The ananepionic substage is at first smooth except for 

 horizontal and inconspicuous growth striae, then becomes longitudi- 

 nally ridged, Fig. 7. 



The changes of form in this substage, which can be divided into 

 three parts, are well marked in these drawings. There is first the 

 age of the cicatrix with a form which is a very elongated trigonal 

 and quite distinct in every way from the next ; then the age in 

 which the broad trigonal form appears, but the surface of the shell 

 is still smooth, and lastly the digonal, longitudinally ridged age 

 passing into the metanepionic and often bounded by a slight con- 

 striction. The metanepionic, Fig. 6, has an elliptical form with 

 longitudinal ridges intersected by the edges of the growth bands. 

 In this the digonal outline tends to disappear, although sometimes 

 it is maintained more or less by the early appearance of the promi- 

 nent, broad lateral ridge. This ridge, however, usually appears 

 later, as shown in section, Fig. 3, and is characteristic of the species. 

 *I have provisionally referred Coelogasteroceras to the family of the Hercoceratidse. 



