LAND AND FRESH WATER MOLLUSCA OF THE EAST RIDING. 1 25 



Lists of species found in the lacustrine deposits of Holder- 

 ness have been given by J. Phillips (Geology of Yorks. 1829: 

 3rd ed., 1875), H. F. Hall (Proc. Liverpool Geol. Soc. 

 1866-7, PP- 38-45). C. Reid (Geology of Holderness, 1885), 

 and the Rev. W. C. Hey (Nat. 12, p. 374). Messrs. Wood 

 and Rome (Quart. Jour. Geol. Soc. 24, p. 154), give 

 genera only, without localities. In August 1892, Mr. 

 F. W. Fierke and myself spent several days in exploring 

 the deposits between Kilnsea and Barmston, and speci- 

 mens obtained then are deposited in the Hull Museum ; 

 we did not find an)' land shells. 



I have not been able to consult the Bootham Observer, 

 mentioned by Mr. R. M. Christy, nor the Yorks. Naturalists' 

 Recorder, referred to by Mr. J. E. Harting in " Rambles in 

 Search of Shells." Neither is included in the British 

 Museum Catalogue. The various publications of the York- 

 shire Societies are in most cases represented in the British 

 Museum Library by odd numbers only, and for this reason I 

 have not seen " Forms of pond snails in Yorkshire," W.C. 

 Hey (Ann. Rep. York Phil. Soc. for 1S83, 1884, pp. 32-35). 

 Doubtless other records exist in the many natural history 

 periodicals which have perished on the via media of popular 

 science and field work, but every effort has been made to 

 render the list a complete summary of all that have been 

 published. 



The East Riding divides naturally into three well marked 

 regions — the Plain of Holderness, the Wolds, and Derwent- 

 land. Full details of the physiography of these divisions 

 will be found in Mr. J. F. Robinson's "Flora of the East 

 Riding ; " roughly they consist of boulder clay, chalk, and 

 alluvium respectively. The rainfall lies between 25 and 30 

 inches per annum over the greater part of the Riding, falling 

 below 25 inches on the Patrington-Spurn peninsula, and 

 exceeding 30 in the neighbourhood of North Grimston and 

 Sledmere. This variation has apparently no effect on the 

 distribution of mollusca. 



From a conchologist's standpoint Derwentland is remark- 

 able for the number of natural and artificial watercourses, 

 which intersect it in all directions. The Ouse on the west, 

 the Derwent and its tributaries, the Foulney, the Market 

 Weighton and Pocklington canals, and the many agricultural 

 drains combine in making it specially rich in aquatic forms, 

 thirty-eight species being recorded for this division, two of 

 which, Viviparus conteclus and Spho?riiim rivicola, are not 

 found in the other two. This abundance has attracted the 



