12 



SCIENCE-GOSSIP. 



INTRODUCTION OF MOLLUSCA INTO BRITAIN. 



Ey a. S. Kennard. 



'TPO all students of the Mollusca the publication 

 -*■ of Mr. H. Wallis Kew's book, " The Dispersal 

 of Shells," was very welcome. For here is a work 

 of about three hundred pages dealing entirely with 

 the mollusca, and there is not a new species or even 

 a new variety described in it ; neither has any 

 attempt been made to alter our old-established 

 names. For these mercies we are indeed thankful. 

 Mr. Kew has here brought together a large number 

 of facts dealing with the means of dispersal 

 possessed by freshwater and land mollusca. 

 Whatever errors there are are those of omission 

 rather than commission ; but in chapter ix., which is 

 headed " On the freshwater and land mollusca in- 

 troduced into the British Isles by human agency," 

 there is much to take exception. It is obvious 

 that the question whether a species is or is 

 not indigenous is best settled by an appeal to 

 the geological record. This Mr. Kew has not 

 done. I will readily admit that the published 

 lists of pleistocene and holocene mollusca are 

 too often unreliable ; but this is not to be wondered 

 at, very few geologists know anything about our 

 recent shells, and, on the other hand, their 

 fragmentary condition does not appeal to the 

 conchologist. But in spite of this much good work 

 has been done of late years, more especially by 

 Mr. Clement Reid and Mr. B. B. Woodward. 

 Mr, Kew first of all states that: "Of the forty- 

 six freshwater species included in the Concholo- 

 gical Society's List of 1883, there are only two, the 

 zebra mussel, Driessena polymorpha, Pall, and an 

 American coil-shell, Planorbis dilatatus, Gould, 

 which can be reasonably regarded as human 

 importations, and, as far as I know, only one 

 other, Sphcerium ovale, Fer., has ever been looked 

 upon as even doubtfully indigenous." 



That Planorbis dilatatus has been introduced there 

 can be no doubt, but this is not so with regard to 

 Dreissena polymorpha, Pall. Mr. Kew has collected 

 the opinions of the " authorities," and we find that 

 with the exception of Gwyn Jeffreys, they all have 

 regarded it as introduced from the Continent. Dr. 

 Jeffreys' opinions, which are set forth in his " British 

 Conchology," conclude with the hope that this 

 species might be found in the upper tertiary 

 deposits in this country. This has now been done, 

 for in Mr. B. B. Woodward's paper, " The Pleisto- 

 cene Mollusca of the London District " (Proc. Geol. 

 Ass., vol. xi, No. 8), it is recorded that Mr. W. J. 

 Lewis Abbott found a single valve of this species 

 at Whitefriars, London, in a deposit ten to fifteen 

 feet from the present surface and which '' most 

 probably accumulated at the mouth of the old 



Fleet ditch, in the early days of the city's existence." 

 Of course a single valve is not much to go upon, 

 and more evidence is wanted ; but there can be no 

 doubt that the introduction of this species is by no 

 means such a certainty as Mr. Kew states. 

 Mr. Jeffreys is the offender with regard to 

 Sphcerium ovale ; it occurs with Planorbis dilatatus in 

 Lancashire, and he thought that it might be 

 Sphcerium Iransversum, Say, but as it is found in the 

 forest bed of Norfolk this opinion is untenable. 

 As to the statement which Mr. Kew quotes that 

 Planorbis glaber, Jeff., is identical with P. parvus, 

 Say, and, like P. dilatatus, introduced, Mr. Dall, 

 after careful comparison of the types, has pro- 

 nounced these species to be different, and P. glaber 

 is one of the most abundant shells in pleistocene 

 deposits. Of terrestrial species it seems there are 

 several whose claims to be true natives are considered 

 doubtful. Testacella maugei, Fer., is considered to 

 be a recent introduction. It has never been found 

 in any deposit in this country, but the same remark 

 applies to its allies, T. haliotidea, Drap., and 

 T. scutulum. Sow. The life-history of these species 

 is such as to render it extremely unlikely to have 

 been entombed in any deposit ; so that at the 

 present, geology cannot help us, and we must wait 

 for further evidence before expressing an opinion. 

 Passing by Stenogyra goodallii, Miller, and Helix 

 elegans, Gmel., both of which have been introduced, 

 we come to Helix pomatia, L. As regards geological 

 evidence it is again negative. It has never been 

 found in any deposit in this country, so that 

 perhaps the view that it is not a native may be the 

 true one. Helix cantiana, Mont., Mr. Kew remarks, 

 " can hardly be looked upon even as a possible 

 importation." But is this so ? At the present 

 time it is one of the most abundant species in the 

 south-east of England, and is found in many 

 other parts of England ; yet in spite of this it is 

 unknown in any deposit even the most recent ; and 

 this has led Mr. B. B. Woodward to express the 

 view that it is post Roman in its introduction, and 

 with this opinion I must concur. Helix cartusiana, 

 Miill, although at the present time restricted to the 

 counties of Kent and Sussex, had formerly a more 

 extended range, as it has been found in an alluvial 

 deposit at Felstead, Essex, so that Gwyn Jeffreys' 

 later view that it was " clearly indigenous " is the 

 correct one. Helix pisana, Miill, shares with 

 H. cantiana and H. pomatia the distinction of being 

 the only helices not found in a fossil state. This 

 fact, and its distribution in these islands are 

 almost conclusive proof that it is not truely a 

 native. With regard to Helix obvoluta, Miill, in 



