Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/580

494 494 A. J. JUXES-UPvOWiN T E's supplementary

GASTEKOPODA.

Apoeehais, Da Costa.

An excellent account of this genus and its fossil forms, hitherto included under the heads of Rostellaria and Pteroceras, is given by Mr. J. S. Gardner in the ' Geological Magazine ' for 1875, Dec. ii. vol. ii. p. 49. He concludes by dividing them into four generic or subgeneric groups, viz. Aporrhais, Omithepus, Tridac- tylus and Dimorpliosoma (torn. cit. p. 394).

Apoeehais maeoinata, Sow.

Rostellaria marginata, Sow. Geol. Trans, vol. iv. pi. xi. fig. 18. Rostellaria Orbignyana, Pictet & Koux, pi. xxiv. fig 4. Pterodonta marginata, Seeley, Ann. & Mag. Nat. Hist. 1861 T vol. vii. pi. xi. fig. 2.

Pterodonta longispira, Seeley, torn. cit. pi. xi. fig. 3.

In the papers above referred to, Mr. Gardner has carefully inves- tigated the history of A. marginata, and has demonstrated its identity with A. Orbignyana, the cause of their separation having been that the lower keel was not clearly shown in the original engraving of the former. This being so, when Mr. Seeley (at p. 283) says of his supposed Pterodonta longispira that it almost as closely resembles A. Orbignyana as P. marginata does A. marginata, it is evident that there cannot be much difference between the two species referred to Pterodonta.

Further, it is to be remembered that both were described from imperfect casts, without any trace of the original shell, so that the characters were necessarily indefinite.

Moreover, from an examination of Mr. Carter's specimens, I am inclined to think that in the case of P. marginata the supposed notch is only an accidentally exaggerated inflection of the concavity below the keel, and that it is not the impression of any definite internal tooth-like ridge.

The figure of P. longispira is stated to be slightly restored from specimens in the same collection ; these, however, appear to have been mislaid, and are not now to be found : I cannot, therefore, say more than that the circular hollow represented in the figure is unlike that caused by the vertically elongated ridge shown in D'Orbigny's figures of Pterodonta, and that the other characters of the figure appear to be those of A. marginata (Orbignyana).

Further evidence must therefore be forthcoming before the pre- sence of Pterodonta in the bed can be regarded as ascertained.

Oenithoptjs, Gardner.

Mr. Gardner has proposed the above name (Geol. Mag. dec. 2 r vol. ii. p. 394) to include the small shells which have hitherto been grouped under the recent genus Pteroceras.

There can, I think, be no doubt that they merited a new generic