MOLLUSCA OF MID-WEST YORKSHIRE. 1 89 



being the Leeds and Liverpool canal from the point at which it 

 enters the county down to Leeds, the river Aire continuing the 

 boundary from that town to its own junction with the Ouse. 



Mid-West Yorkshire, although quite destitute of sea-board, 

 is a highly diversified tract of country, including the whole of 

 the drainage-basins of the Nidd, the Wharfe, and the Wash- 

 burn, the northern strip of the whole length of the Aire Valley, 

 the upper basin of the Ribble, and a small part of the valley of 

 the Ure. In point of level it ranges from 2414 feet at Whern- 

 side and 2373 feet at Ingleborough, down to the flat alluvial 

 districts of the plain of York, scarcely if at all above sea-level. 

 Geologically it includes rocks of palaeozoic age in its mountain- 

 masses, carboniferous limestones followed by millstone grit and 

 coal measures occupying much of its western and mid area. 

 The belt of Permian limestone crosses the vice-county from 

 north (at Staveley) to south (at Fairburn), and the eastern 

 portion of the district is occupied by glacial drifts overlying 

 the Triassic and diluvial rocks of the vale (or plain) of York. 

 The central axis of drainage of Great Britain passes through the 

 vice-county, the Ribble draining westward into the Irish Sea, 

 while the other streams of the district flow east into the estuary 

 of the Humber. 



With so diversified an area to inhabit, the fauna is rich, as 

 the present and succeeding lists will show. In fact specimens 

 have been shown from so many localities that it is necessary 

 in the case of some of the common species to give generaliza- 

 tions and omit the detailed records upon which they are 

 founded. 



The collectors to whom the society is indebted for the 

 sight of the specimens upon which this paper is exclusively 

 founded are the following : — Thos. W. Bell, M.C.S. (Leeds), 

 J. D. Butterell, M.C.S. (Beverley), James Carter (Masham), 

 W. Eagle Clarke, F.L.S. (Leeds), H. Crowther (Leeds), James 

 Ingleby (Eavestone), W. Nelson, M.C.S. (Leeds), H. Pollard 

 (Leeds), Thomas Pratt (Ripon), W. Denison Roebuck, P\L.S. 



