452 Sir H. H. Howorth — Geological History of the Baltic. 



group of species, especially if we are tied down to some theory 

 which has to be supported at all costs and which distorts our vision 

 when we look the facts in the face. It is only too easy to select 

 a number of shells which seem to thrive as well in the Scandinavian 

 or British seas as in the Arctic Ocean, to dub them Arctic and 

 then to apply the term Glacial to a deposit. Again, even the best 

 of the older conchologists have at times failed to discriminate 

 small differences and varieties which may entirely sophisticate the 

 conclusion. I will quote a good example which happens to be very 

 familiar to me because I wrote a monograph on the shell, viz. Mya 

 arenaria, which was published in the Proceedings of the Zoological 

 Society.^ There can be no doubt from the evidence that M. arenaria 

 is a new addition to the fauna of the North Sea and its outliers. 

 There is no evidence that it existed there before the beginning of the 

 seventeenth centurv. It was first described by Lister in 1678. 



Gwyn Jeffreys, who did not know this, in his account of the 

 Molliisca of the Uddevalla raised shell-bed, not only clairned to have 

 found this species of Mi/a there, but made a somewhat characteristic 

 deduction in regard to it. He described it as an Arctic shell, and 

 says of it, " The occurrence of this circumpolar shell- fish so near the 

 Tropic of Cancer probably indicates the most southern limit in space 

 of the Glacial epoch " (British ConcJiology, iii, pp. 65-6). 



Jensen, a much more critical person than Gwyn Jeffreys, has, in 

 fact, pi'oved most completely that M. arenaria is not an Arctic shell 

 at all and does not exist in the Arctic regions. Gwyn Jeffreys 

 had mistaken another and very different species with an entirely 

 different habitat for it, namely M. truncata, var. ovale, which is 

 a very high Arctic shell and has been found in Iceland, Greenland, 

 Spitzbergen, Nova Scotia, and the Kara Sea. The mistake of Gwyn 

 Jeffreys was a particularly unfortunate one, because it was copied 

 into several geological works and made the basis of several most 

 illegitimate deductions. (For details of the whole discussion I must 

 refer to niv paper in the Proceedings of the Zoological Society, 

 1909, pp. 745-67). 



On several other occasions, as it seems to me, Gwyn Jeffreys used 

 the word "Arctic" as applied to the habitat of certain shells from 

 the raised beaches in a very arbitrary way. 



It does not follow, again, that when truly Arctic shells are found 

 in more southern waters they should be always dubbed as Arctic. 

 Before so naming them we must be careful to consider measurements 

 and other differentise. Manjr Arctic shells occur in our Northern seas 

 which only attain their normal and typical size in very high latitudes 

 and become dwarfed in size and otherwise modified further south. 

 There are others which ought not to be called Arctic at all, because 

 they thrive just as well in temperate regions as they do in Arctic 

 ones, having the adaptability of Scotchmen. So that considerable 

 care and judgment are required in order to justify the application of 

 the term " Arctic" to groups of Northern shells. 



^ " Some living Shells, their recent Biology, and the light they throw on the 

 latest Physical Changes in the Earth [Mya arejtaria]," by Sir H. H. Howorth 

 (Proc. Zool. See, 1909, pp. 745-67). 



