. L'Annals and magazine of natural history ; zoologie, botanique, et de la géologie. L'histoire naturelle, zoologie, botanique, géologie. Une nouvelle classification des Ammonites. 367 fonction de l'Aptychiis Anuptjclius, estime que l'a servi d'opercule : il se produit, cependant, dans la même position que. A. stcraspis : figure tirée de Waagen, PaloDont. xvii. pi. 40. f. 4. l'ancien de ces organes * ; et il est donc évident qu'il a accompli le même but. La fonction de l'Aptychus étant ainsi déterminé, la fourrure- nishes d'un point important pour la détermination de l'arrangement relatif des organes en t

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. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. a new Classification of Ammonites. 367 function of the Aptychiis, believed that the Anuptjclius served as an operculum: it occurs, however, in the same position as. A. stcraspis: figure taken from Waagen, PaloDont. xvii. pi. 40. f. 4. the former of these organs * ; and it is therefore evident that it fulfilled the same purpose. The function of the Aptychus being thus determined, fur- nishes an important point for the determination of the relative arrangement of the organs in the Ammonite, which maj be deduced from that which they occupy in the Nautilus. In this animal the nidamentary gland is situated on the sijjhonal side above the adductor muscle, and outside of the ring of adherence. It is only natural to suppose that the relations of these various organs were the same in the Ammonite. Direct observation serves here to confirm the theory. Oppel has remarked in a great number of Ammonites from the limestones of Solenhofen a mark of a peculiar form (Paliiont. Mittheil. pi. 69). M. Waagen has ascertained that this im- pression has precisely the same shape as that of the ring of adherence in the Nautilus (see the foregoing sketch); it is the trace of the horny margin of this ring, which has been preserved in consequence of the tranquillity of tlie deposition of the sedi- ments. This trace begins at the margin of the aperture, about in the middle of the sides, follows the spiral of the shell back towards the septum, and then bends forward towards the siphonal side. The Aptychus is above and outside of this * See A. planorbis, Sow., in Waagen, Palseontogr. 1869, xvii, pi. 40. fi{r. 5.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. London, Taylor and Francis, Ltd

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