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ventrodorsal .30 mm. at the termination of the same, the fragment 

 of the living chamber also devoid of shell was transversely about 

 40 mm., while the dorso-ventral had increased to 32 mm. This 

 and the point of view of Fig. 18 gives the aspect of a more con- 

 siderable diminution in the lateral diameters than actually took 

 place. The sectional view of this end shows true proportions in 

 Fig. 19, PL vii. 



The section, Fig. 15, gives the neanic whorl at the inner break in 

 the side view, Fig. 13, and this shows how very small and slight the 

 zone of involution is in this species. It broadens slightly with age, 

 but immediately disappears in the free part of the whorl, as it does 

 also in most species of this genus. 



The lines of growth are given on the dor. c n of the metagerontic 

 substage in Fig. 17, and these do not dirTti materially from those 

 of the nepionic stage in Estonioceras perforatum. The lines of 

 growth could not be observed on the dorsum of the earlier stages 

 of growth, but it is probable that in the stages in which the whorls 

 are in contact that the dorsal crest is narrow and occupies the area 

 of the impressed zone. 



The sutures in the paranepionic substage have ventral saddles 

 with very slight ventral lobes on either side, saddles at the lateral 

 angles and apparently lateral lobes. Three sutures of this substage 

 were followed on the dorsum to the centre and no central inflec- 

 tions could be seen. This was somewhere about the sixth or 

 eighth septum, as nearly as could be ascertained, and the suture 

 formed a very shallow lobe across the dorsum, but this would 

 ordinarily be described as straight. These, in other words, are 

 closely similar and of about the same age as the complete dorsal 

 sutures of Estonioceras imperfectum given in Fig. 21, PI. vii, and 

 probably about the same age as the dorsal sutures of Estonioceras 

 perforatum given in Fig. 12, PL vii. In the ephebic stage broad 

 lobes appear on the venter, reaching to the saddles at the lateral 

 angles. The septum, Fig. 150, PL vii, given to show the contact 

 furrow, also shows that a faint narrow dorsal lobe coextensive 

 with this furrow is produced by contact. In the paragerontic 

 substage, as shown on the last three sutures of Fig. 18, the broad 

 ventral lobe is replaced by faint saddles with very faintly marked 

 lobes on either side and the saddles of the lateral angles in conse- 

 quence of the rounding of these angles have become lateral saddles. 

 The lateral lobes appear only very faintly or are absent on the 



