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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



am unable to do, they will not materially interfere with our deter- 

 mination, and their lithological character will remove all doubt as to 

 the possibility of their being derivative fossils. 



"The accompanying list contains the names of those species to which 

 they bear a very close resemblance. I give them as approximations 

 only ; and, although there is not one which without a doubt could be 

 satisfactorily determined, I still think that, taken collectively, they 

 are such as to justify a probable assignment to one of the Crag periods, 

 and they appear to have been inhabitants principally of the Coralline 

 zone. In reviewing this list it will be observed that there is a large 

 preponderance of bivalves, and many of the individual specimens 

 belong to the genera Nucula, Leda, and Area, with a hinge charac- 

 terized by a linear series of teeth or denticulations, and of a magnitude 

 approaching what may be called an Arctic Fauna, accompanied with 

 several species of Astarte, &c, generally considered also of a Boreal 

 character ; and these might perhaps incline us to assign the deposit to 

 the age of the Red Crag : — 



Cliona. 



Balanus(?). 



Lunulites. Coronula(P). 

 Diadem a ? (species of). 

 Terebratula grandis ? 

 Pecten avicula ? 

 Modiola modiolus ? 

 Area lactea ? 

 Leda myalis ? 

 Nucula nucleus ? 

 Cardium (with spines). 

 Cardita. 



Lucina or Diplodonta. 

 Kellia or Lepton. 

 Isocardia. 

 Astarte digitaria ? 

 pygmaea ? 



Astarte Omalii ? 



compressa ? 



Cythera rudis ? 



Venus ? 



Tellina donacina? or Donax. 



Mactra triangulata? 



Anatina. 



Panopaea ? 



Dentalium costatum ? 



Emarginula reticulata ? 



Trochus. 



Natica. 



Rissoa ? 



Seal aria subulata ? 



Nassa prismatica ? 



Pyrula ; 



with a few others I have not been able to determine*. 



"There is, however, in the Coralline Crag somewhat of an anomalous 

 collection of shells, many of which are peculiar to the Arctic seas of 

 the present day, while some of their associates are found only in the 

 Mediterranean or the South of Britain ; and, although there are amongst 

 Mr. Prestwich's fossils many which resemble Red Crag species, there 

 is not one, with the exception of Leda myalis (and this is but a doubt- 

 ful identification, as I have not been able to see the exterior), that 

 might not also be considered as belonging to the Coralline Crag. 

 I believe they may with more propriety be considered as the 

 equivalent of the Older Crag, more especially as there is one speci- 

 men which has every appearance of being the cast of a true Pyrula ; 

 and, although this genus has also been procured from the Red Crag, 

 I believe the specimens so found to be derivative fossils, and not to 

 have belonged to that period. In looking at the list of genera, it 

 will not, I fear, afford much assistance in the determination, as the 



* Mr. Searles Wood has since added, with a doubt, a Phorus, which he thinks 

 may be related to Trochus cumularis, Brongn.,and Pectunculus glycimeris, although 

 the latter, he says, might be the Vicentin variety of P.pulvinatus. See also p. 332. 



