136 Shells of the Holdemess Basement Clays. 



are more than one species so called. This seems to be so at 

 Bridlington where the N. insignis Gould is common. It also 

 occurs in the Chillesford beds. Wood's figure seems to differ 

 in shape (not sculpture) from Sowerby's type, as it also does 

 from the fully adult A. lyalli. 



Woodward remarks that the Bridlington shells differ from 

 those of the Crag in a tendency to become smooth when ap- 

 proaching full growth. Such is the case with the few frag- 

 ments of this shell I obtained from the Wexford gravels. 



Note E. — Ostrea celtica* — Oysters are rare in the Brid- 

 lington group. The best I have seen is the one in the York 

 Museum, H. 60 mm., B. 45 mm. It is not well preserved, but 

 appears to be of the same type that occurs at Bohuslan and in 

 the Shetlands, where it is nearly extinct — as it is in most 

 localities in the north where formerly abundant, i.e. W. Scotland. 

 It is not the 0. edtdis of Linne, the type of which in the Linnean 

 Society's possession is the 0. cristata of southern authors, and 

 ranges in a living state from Bohuslan to the Mediterranean, 

 via the West Coast of Ireland. Pending a memoir on the 

 British Oysters, I have named the northern form A. celtica 

 to distinguish it from the Linnean shell. Jeffreys seems to 

 have been misled in giving Iceland as a locality, as his authority, 

 Mohr!, 1786, is only quoting from an earlier work by Olafsen, 

 1772, who, in his turn remarks, ' but we have not seen it.' 

 (Jensen op. cit.). So far as I can see, after a careful examina- 

 tion, this type of oyster has only a cousinly relation to its 

 pliocene predecessor. 



The shells vary very much as regards preserva.tion. In the 

 body of the clay they are, or were, often preserved in places. 

 In others, while the contour of the shell is unaltered, the 

 shell itself has been separated into many fragments, much as 

 if the shell had been broken in situ, and the edges ol the frag- 

 ments contracted after breakage. This disjunction seems to 

 be the cause of so many loose pieces remaining after washing. 

 Mr. Headley, writing to me, says ' The shells in the clay seemed 

 broken in place and the edges were sharp.' In the sand 'the 

 edges were worn and broken.' 



The clay is very homogenous and is regarded by Mr. Lamp- 

 lugh as a true glacial mud. Its origin I suggest to be due 

 in large measure to muddy streams or to ' large volumes 

 of water issuing from the edges of the ice upon the escarp- 

 ment,' (Lamplugh), some miles to the N. East. R. Brown, 

 Physics of Arctic Ice, Q.J.G.S., 1870, p. 671, noted from 



* Mr. Reid records a bed of double Oysters from above the Weybourne 

 Crag, near Lower Sheringham, N. of Weybourne, and apparently on a 

 level with the Leda myalis bed. 



Naturalist, 



