The Quarterly journal of the Geological Society of London . inmany other ammonites. The conditions in Clymenia (Palyeonto-graphica, pt. 2, vol. xxvii, 1880, pi. viii) are exceptional, for thedorsal folds are more deeply divided than the ventral. The factthat in it the si2)huncle is dorsal suggests that the complexity offolding is, in some way, associated with the position of the siphuncle. XI. Septal Sectiois^s of DACTVLiocEiiJS. In the foregoing pages it has been shown that the central area ofan adult septum is strikingly similar to the earlier septa. This factsuggests that, if septal section
The Quarterly journal of the Geological Society of London . inmany other ammonites. The conditions in Clymenia (Palyeonto-graphica, pt. 2, vol. xxvii, 1880, pi. viii) are exceptional, for thedorsal folds are more deeply divided than the ventral. The factthat in it the si2)huncle is dorsal suggests that the complexity offolding is, in some way, associated with the position of the siphuncle. XI. Septal Sectiois^s of DACTVLiocEiiJS. In the foregoing pages it has been shown that the central area ofan adult septum is strikingly similar to the earlier septa. This factsuggests that, if septal sections were made, they would show someresemblance to the suture-lines at different stages in develo])ment. Fig. 10 (p. 43) shows a series of such sections made at the zonallines shown in fig. 11. Thus section I) represents the ground edgeof the septum at zonal line 2 of fig. 11 (p, 44). This illustratesthe extraordinaiy flatness of the innermost area of the septum. Fig. 9.—DeveJo2)ment of the suture-Une (>/Dactyliocerascommune {Jigured in PI. II, Jig. 2).. a=First suture X Second suture X Seventh suture X 28 d = Sutm-e at 1| whorls X 28. j; = Suture at 4| whorls X = Suture at 2f whorls x 15. /)= Suture at h^ whorls X Suture at 3f whorls X 12. / = Sutiu-e at 6f whorls X 2, i Fig. 10.—Series of septal sections made from one of the latestsepta of the Dactvlioceras/y/^r*?^/ in PL II, ff/- ^- X 2.
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
