126 HULL SCIENTIFIC AND FIELD NATURALISTS' CLUB. 



attention of several West Riding conchologists, and the 

 neighbourhood of Howden, Wressle, and Newport has been 

 well searched for aquatic species by Messrs. G. Roberts, 

 J. Beanland, and Wm. Nelson, but probably for the same 

 reason terrestrial mollusca have been in most cases neglected, 

 and we have few records of the smaller land species. An 

 additional reason may be found in the fact that the " waste " 

 land of this division, though more extensive than in the other 

 two, consists of large sandy commons whose molluscan 

 fauna may be concisely enumerated as in the Skipwith 

 circular (124), " no mollusca are to be found on the common 

 itself." Yet, granting this, it is not obvious why alluvium 

 shall be less productive than boulder clay ; and the absence 

 of records may be attributed to lack of workers rather than 

 to a real difference in distribution. Of the northern and 

 central portions of Derwentland very little has been recorded. 

 The mollusca of York and district have been tabulated many 

 times, and few works on British Conchology fail to cite 

 York as a locality for rare species, but the majority of 

 recorders have preferred to follow Dr. Martin Lister in the 

 North and West rather than the East Riding. General 

 records for the Ouse below York have been included here ; 

 a more exact investigation may remove them from the East 

 Riding list. No records have been found for that part of 

 the valley of the Derwent which lies to the north of the 

 Wolds. 



In the central division, which includes all the elevated 

 land of the Riding, aquatic mollusca are rare since the 

 porosity of the chalk precludes the formation of natural ponds 

 and the artificial ponds are usually barren or contain Pisidia, 

 L. peregra, and L. truncatula only. Its list of aquatic 

 species, however, reaches 30, chiefly from the ponds on the 

 boulder clay in the neighbourhood of Filey and Flamborough, 

 and it has its own peculiar form in Ancylus fliivia tilts ; which 

 is almost confined to the small streams of its slopes. The 

 numerous dales, chalk pits, and beech woods make this 

 region richer in land species than the other two, and even fir 

 woods on chalk are not barren : Clausilia laminata, Pupa 

 augliea, Limax chiereo-niger , Limax arborum, and Amalia 

 soiverbyi are found in this division only, while Helix 

 granulata and Clausilia ritgosa have only been found outside 

 it at Wressle and Langwith respectively. It is characterised 

 by the presence of Helix rujescens and Clausilia, and the 

 relative abundance of Helix liorteusis, H. arbustorum, and 

 H. itala. The investigation of this area commenced with the 



