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 



