On Species &• Varieties in Birds. 143 



In these islands a peculiar melanistic variety of the 

 Blackcap also occurs, which, so far as I know, has not been 

 observed elsewhere, and which has been described as a 

 distinct species under the name of Sylvia heinkeni, but which 

 later research has proved to be only an accidental and not a 

 constant variety, one out of a brood of ordinarily coloured 

 birds in the same nest being of this dark tint of colour. 



A curious circumstance that has been frequently remarked 

 on is the strange similarity between the avifauna of Japan and 

 Western Europe. Amongst the species common to Japan 

 and Europe I may enumerate the following : Parus pahistris, 

 Bonasa betulina, Picus major, Picus leuconotus, Gecinns 

 canus, Dryacopus martins, Nucifraga caryocatactes, Acredula 

 candata, Coccothraustes vulgaris, and Alatcda arvensis, besides 

 which several European species are there represented by 

 closely allied forms, as for instance Cyanopica cooki by 

 Cyanopica cyanea. Troglodytes parvulus by Troglodytes fumi- 

 gatiis, Regulus cristatus by Regtdus japonicus, and Erithacus 

 rubecula by Erithacus akahige. A very remarkable circum- 

 stance is that there are but two species known of Cyanopica, 

 a genus so very distinct in colouration, one found in Japan 

 and Eastern Asia, and the other in Western Europe, these two 

 being so closely allied that many naturalists do not separate 

 them, and in the vast intervening tract this genus is unrepre- 

 sented. Doubtless at some remote geological period these 

 birds were identical, and in the course of time the one form 

 has been driven out to the east, and the other to the west, and 

 the parent stock has become extinct. 



However, I have now considerably exceeded the time 

 allowed me for my remarks on the subjects I have treated of, 

 and must now close, trusting that, though crudely strung 

 together, the facts I have mentioned will tend to throw some 

 little light on the extreme difficulties that are in the way of 

 defining where the limit is, between a mere variety and a 

 species. 



32. — On the Mollusca of the Club District. 



By Mr. Kenneth McKean. 



Read i^th September, 1882. 



This branch of zoology has hitherto not received much 

 attention at our meetings. The only paper we have had on 

 the subject was read by Mr. G. F. Linney, ^!f\h. September, 

 1871, "On the land and fresh water shells of the Croydon 

 district." The aim of that excellent little paper was, however, 



