NOTES ON THE CAMBRIDGE GREENLAND. 495
designation, and that they do not properly belong to the family of the Strombidse at all. The Aporrhaidse (with which they are now classed) should, I think, constitute a distinct family, intermediate between Cerithiadae and Strombidse, and probably representing the branch from the former which led to the development of the latter.
Ornithopus retusus, Sow., sp.
Rostellaria retusa, Sow. Geol. Trans, ser. 2, iv. pi. xviii. fig. 22.
Rostellaria bicarinata, Desh. Mem. Soc. Geol. Er. vol. v. pi. xvii. fig. 14.
Pteroceras globulatum, Seeley, Ann. & Mag. Nat. Hist. 1861, vol. vii. pi. xi. fig. 1.
(?) Aporrhais bicornis, Pict. & Camp. Ste. Croix, 1864, pi. xciv. figs. 8, 9.
In the ' Geological Magazine,' 1875, p. 52, Mr. Gardner carefully describes this species, and calls attention to the great resemblance between it and that figured by Pictet and Campiche under the name of A. bicornis.
With regard to P. globulatum, I was inclined to look upon it as a distinct form, and communicated this opinion to Mr. Gardner in 1875 ; I have since had the opportunity of inspecting the specimens in Mr. Carter's large collection ; and these have convinced me that P. globulatum should be considered as a dwarf race of 0. retusus.
I believe therefore that, although one or more of the above- mentioned forms may be viewed as a definite local variety, yet, the same specific description being applicable to all of them, they should be regarded as constituting a group, of which 0. retusus may be taken as the type.
Ornithopus histochilus, Gardn.
Aporrhdis histochila, Gardner, Geol. Mag. 1875, pi. vii. figs. 5, 6.
In March 1875 I forwarded to Mr. Gardner some casts from the Cambridge bed, which had been referred to Pteroceras Fittoni, asking him at the same time whether this species had ever been obtained from the Gault. This question he answered in the negative, but remarked at the same time that although the specimens sent were very like P. Fittoni, yet they still more closely resembled an undescribed form from the Upper Greensand of Devizes which he intended shortly to investigate. The result of his researches appeared in the July number of the Geol. Mag., where he figured and described this form under the name of Aporrhdis histochila, noting its occurrence in the Upper Greensand at Cambridge, and in the Gault of Folkestone.
The species is allied to A, Fittoni and A. retusa, Mr. Gardner including them all in his proposed genus Ornithopus. Thus, there- fore, another Cambridge form proves to be identical with a Gault species, though in this case it happens to be found in the Upper Greensand as well.
