1881.] Hordiuell Cliffs, Hampshire. L51 



Notes on some of the Fossils. 



Marginella simplex, Edw. This is cited only from Long 

 Mead End in Edwards' Eocene Mollusca, Univalves, p. 144, but in 

 his collection in the British Museum is a specimen labelled as 

 from Colwell Bay ; from an examination of the matrix in which it 

 was imbedded we think this latter also from Long Mead End. 



Pisania lavata, Sow. A variety with a secondary thread be- 

 tween the larger spiral ones in addition to still finer ones ; it 

 occurs in the Barton beds also with the type. 



Natica abscondita, Desh. One specimen agrees exactly with 

 French specimens which I collected in the equivalent bed near 

 Mortefontaine, Paris basin : the shell is punctate. I cannot find 

 any punctations in N. Studeri, this is the readiest means of 

 distinction ; our shell is also shorter and broader relatively, and 

 the spire more inclined to be turriculate from increased flattening 

 of the younger whorls at the suture. 



-AT", labellata occurs in the Beacon Bunny bed below and in the 

 Middle Headon above, but we do not happen to have found it in 

 the intermediate W. Bagshot sand. 



Cerithium pleurotomoides, Lam. This shell has with us hitherto 

 been determined as G. concavum, Sow., and considered identical 

 with it. It was the identification of this latter shell with Lamarck's 

 species which led some observers to correlate the Middle Headon 

 with the fossiliferous zone of Mortefontaine, or uppermost part of 

 the " Sables de Beauchamp." However, M. Munier-Chalmas has 

 discovered the distinctness of these two species, and the fact of 

 their occupying different horizons. By comparison of Long Mead 

 End specimens with French examples from near Mortefontaine 

 we recognise their identity, and so establish a perfect correspond- 

 ence between the French and English series. Thus C. concavum 

 characterises the M. Headon of Headon Hill, Colwell Bay, and 

 Hordwell, while C. pleurotomoides is found only in the Upper 

 Bagshot sand of Long Mead End. 



The most ready way of distinguishing these species is the 

 curve of the aperture or sinus of the outer lip, which curve also 

 persists in the growth lines which mark successive apertures : in 

 G. concavum the sinus is deeper so that the lines above and below 

 it meet at an angle of rather less than 90°, while in G. pleuroto- 

 moides the angle is considerably over 90° or even 100°. The 

 ornaments in Long Mead End examples are rarely well enough 

 preserved to make them available for ready distinction. 



G. pyrgotum, Ed. MS. We have several examples of a shell 

 so determined by Edwards in his collection, in some points how- 

 ever it is more like C. mutabile, Lam., a Bracklesham shell than 



11—2 



