POPwTLAND EOCKS OP ENGLAND. 217 



Ceritbium portlandicum (Sow.). 



Hudlestoni (Blake). 



Orthostoma acaticarina (Blake). 

 Pleurotomaria rugata (Ben.). 

 Pleuromya tellina (Ag.). 



Yoltzii (Agf.). 



N eeera portlandica ( Cott.). 

 Corbula dammariensis (Buv.). 

 Lithodomus, sp. 

 Astarte rugosa (Sow.). 

 Cyprina implicata (JDe Lor.). 



elongata (Blake). 



Cypricardia costifera (Blake). 

 Lucina portlandica (Sow.). 



minuscula ? (Blake). 



Anisocardia pulchella ? (Be Lm\). 

 Cardium dissimile (Sow.). 

 calcareum (Blake). 



c. Trigonia gibbosa (Sow.). 



inciirva (Ben.). 



Pellati (Be Lor.). 



tenxiitexta (Lye.)?. 



Area Beaugrandi (Be Lor.). 



Nucula depressa (Blake). 



Mytilus autissiodorensis ? (Cott.). 

 c. Perna Boucbardi (0pp.). 

 c. Pecten lamellosus (Sow. . 



SLiprajurensis (B'Orb.). 



Lima rustica (Sow.). 

 c. Ostrea expansa (Sow.). 

 c. bononiae (Be Lor.)- 



Exogyra bruntrutana (Thurm.). 



Plicatula ecbinoides (Blake). 



Serpula quinquangularis (Gold/.). 



Echinobrissus Brodiei^, (Wr.). 



The most characteristic of these is the little Natica ceres, which 

 marks an horizon in the true Portlandian of Boulogne. The other 

 Naticce mentioned by De Loriol as found here by M. Ssemann come 

 from the Boulognian grits ; I have not been able to see any thing 

 like them in Buckinghamshire. Of the fossils usually occurring in 

 higher beds Ce7'ithium portlandicum is only common in one place. 

 iMcina portlandica and Astarte rugosa are rare. The first of these 

 three seems always to be commonest in the uppermost beds of a loca- 

 lity, whatever their age ; perhaps its presence is a sign of approaching 

 freshwater conditions. The Cardium is the true dissimile., and not 

 Pellati, which occurs abundantly below. The larger oysters are 

 abundant ; and the Plicatula is not rare. De Loriol mentions Serpida 

 coacervata as common on the shells from this district ; but the 

 common Serpula is not that species, which I have seen nowhere from 

 Portland rocks ; it is not even S. gordialis, but a carinated species, 

 which becomes abundant below. 



Ko. 3. Throughout the whole district there is, underlying these 

 limestones, a bed of yellowish brown sand, which is blue when first 

 extracted. It is not at all glauconitic, and contains but few fossils. 

 Towards the north, at Quainton, there is at the base a Serpulite, the 

 species being S. quinquangularis ; it does not form a hard rock, and 

 reaches a thickness of 2 feet. The nearest spot to this at which 

 this portion of the series is seen again, viz. Coney Hill, shows this 

 to be very local, as it has diminished to 6 inches, and is not solely 

 composed of Serpnlce. The whole thickness, however, a little under 



5 feet, remains the same ; and I have nowhere seen more than 



6 feet. The only interest attaching to this bed is its constancy, 

 and the fact that it occurs within the limits which we must assign 

 to the Portland Stone as distinguished from the Portland Sand. 



1^0. 4. This is a mass of rubbly limestone of very peculiar cha- 

 racter, seen admirably in the quarries towards the north. Dr. 

 Fitton mentions it in his section at Quainton as the " middle rock 

 and rubble, abounding in fossils." It may still be seen there ; but 



* Fide Mr, Brodie. 

 Q. J. G. S. ^0. 142. Q 



