265 

 THE CONCHOLOGY OF MALHAM. 



W. DENISON ROEBUCK, F.L.S., 

 Hon. Secretary and Recorder to tite Conchological Society. 



This paper is not a record of personal experience, for I have had 

 scarcely any in the Malham district (as the meagreness of the list of 

 slugs will show), but simply a transcript of records which have been 

 authenticated during the past twelve years by the referees of the 

 Conchological Society ; and it is thought the publication of them 

 will be of interest in connection with the approaching excursion of 

 the British Association. 



The district included in the present paper is the plateau of 

 Malham Moor, on which is situated the largest of the few lakes of 

 which Yorkshire is able to boast, and which has a general elevation 

 of about 1,300 ft., together with the steep escarpment (formed by 

 the South Craven fault) which terminates it southwards, and so 

 much of the upper valley of the Aire as extends from the escarpment 

 to Bell Busk. This is in the main — so far as mollusca are concerned — 

 a limestone or calcareous area, and therefore produces in profusion 

 such species as Helix rupestris, H. arbustorum, If. ericetorum, 

 H. lapicida, Balea perversa, and Clausilia dubia. The mollusca 

 which inhabit the Tarn itself are worthy of remark. The altitude 

 (1,300 ft.) is a great one at which to expect to find such species as 

 Limncea stagnali's, Valvata piscinalis, Bythinia tentaailata, Planorbis 

 nautileus, P. contortus and Sphceriuni corneum, but the interest is 

 increased when we find that some of these species — notably the 

 L. stagnalis — are marked by white streaks in somewhat regular 

 alternation with the horny ground colour of their shells, a pheno- 

 menon which American authors in treating of similar instances in 

 the Rocky Mountains States ascribe to the alternations of cold 

 and warmth to which water-shells are necessarily subjected in 

 localities lying at so great an elevation as Malham Tarn does in 

 comparison with the localities in lowland plains usually occupied by 

 such species. The specimens of Ancylus fluviatilis which are found 

 in the cold waters of the Aire just at the point where it issues — a full 

 stream — from the base of Malham Cove, are also remarkable for 

 being opaque white in colour. The marshy ground (Malham Tarn 

 Moss) lying on the western side of the Tarn is productive of various 

 damp-loving species. 



It will be unnecessary to mention here the names of those 

 observers to whom we are indebted for what we know of the 

 mollusca of Malham, inasmuch as I have adopted the more satis- 



Sept. i8qo. 



