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. 



