Mr. S. V. Wood's Catalogue of Shells from the Crag. 457 



ledge of the contents of these beds which would enable us to 

 determine with precision the number of species each forma- 

 tion possesses. I give ray Catalogue more to show the riches 

 of our tertiary deposits than with the expectation that any 

 generalizations can be established where so many sources of 

 error are likely to interfere with our calculations, hoping that 

 a better acquaintance with recent British Testacea will enable 

 me at a future period to correct some of the errors it may 

 probably be found to contain. Many of the identifications in 

 this Catalogue have of necessity been based upon figures and 

 descriptions, but a comparison with the specimens themselves 

 is in all cases essential to correct determination. 



With respect to the temperature of the sea during the for- 

 mation of these deposits, various and conflicting opinions 

 have been given. The coralline crag, it has been asserted, pre- 

 sents us with indications of a tropical nature ; a conclusion 

 which has been drawn from the profusion of Polyparia that 

 this formation contains. In regard to the evidence given by 

 the presence of Testacea, it has been imagined on the one 

 hand, that such genera as Glycimeris, Trichotropis, Astarte 

 and Cyprina, and the large development of these latter forms, 

 give reason to conclude the climate was at least as cold as 

 what we experience at the present day ; but it may be re- 

 membered that Astarte and Cyprina are both found in the 

 London clay associated with shells whose analogous forms 

 are only now living in tropical climates, and that the Glyci- 

 meris has been found upon the coast of Massachusetts ; on the 

 other hand, the Pyriila are all denizens of the Oriental seas, 

 and the only species of Pholadomya yet known was procured 

 near one of the West India Islands ; these favour the assump- 

 tion that the sea of the crag period was of a warmer tempe- 

 rature. Several of the species of the coralline crag have been 

 found living in the Mediterranean, and as far as we know at 

 present restricted to that part of the world. It is strange to 

 find associated in the same formation such apparently incon- 

 gruous types as Pyrula and Pholadomya, Glycimeris and As- 

 tarte, the one representing the tropical form, while the other 

 is generally found in the North ; but if we only give a little ex- 

 tension to the geographical range of each of these types, al- 

 lowing what are generally considered to be northern genera to 

 reach as far to the southward as we would give the same in- 

 dulgence to those that appear exclusively of a tropical cha- 

 racter, it would approximate the latitude and probably the 

 temperature of that great inland sea or that of the coast of 

 Portugal, to which I would assign the temperature of the 

 Ann. ^ Mag. N. Hist. Vol. ix. 2 H 



