NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 23 



The Rev. W. C. Hey says : " dead shells occurred at Ful- 

 ford two years ago, but none since, I believe. I fear it is now- 

 extinct." 



Dr. E. Lankester found this species in ditches near Askern, 

 about 1842, and Mr. H. Shaw, of Leeds, in 1881 found several 

 dead but fresh specimens in the stream running from, and in the 

 pool there. Subfossil shells of a dwarf and stunted form are 

 thrown up by the moles in the fields about Askern. 



The species is however not yet extinct in Yorkshire, and its 

 claim to be regarded as a member of the Yorkshire fauna has 

 been re-established by Mr. W. Eagle Clarke, who in company 

 with Mr. W. Denison Roebuck, succeeded in finding a speci- 

 men in the Gravel Drain on the Lincolnshire border in April, 

 1883, whilst engaged in a special search for it. 



All the Yorkshire specimens we have hitherto seen are 

 dwarfed in size and are hardly one-third of the volume of some 

 of the same species from Lancashire localities. 



This species, according to the observations of Mr. T. 

 Ball, of Brigg, hibernates socially. "In almost every case where 

 a specimen could be seen, there was in reality a considerable 

 number all huddled together and buried in one common hole." 



Dr. Jeffreys, at p. 36 of British Conchology, says " the 

 epidermis of the last formed whorl in the young shell, when it 

 leaves its mother, has three transverse rows of recurved bristles, 

 which in after growth are replaced by the colored bands that 

 encircle adult shells, the formation of these bands as well as 

 of the bristles being caused by different organs which are suc- 

 cessively developed in the same part of the mantle." According 

 to our observations this is hardly correct. The three spiral 

 lines of bristles encircle the last whorl, and the two upper lines 

 are continued on all except the apical whorl. The color bands 

 are present at and before birth and not afterwards developed. 

 In addition also to the brownish bands there are three some- 

 what irregular blackish bands on the mantle and plainly visible 

 through the transparent shell, formed of a number of blackish 



