35(> 



Geographical Distribution of Mollusca. 



being a species of later date. Of those in the reed-belt L. 

 palustris is recent and does not occur in the marl ; Bithynia 

 tentaculata is abundant, living and in the fossil state ; Planorbis 

 contortus sparingly fossil and recent. 



The following shows the probable grouping of the marl 

 species. 



Reed Belt. 



Open Water 



L. pereger Miill. 

 Planorbis albus L. 

 ,, crista L. 



Valvata piscinalis Miill. 



Marsh. 



Pisidiitm pHsillium 



Gmelin 

 obtusale Pf. 



B. tentaculata L. [foot. 

 Planorbis fontanuslAght- 



,, contortus L. 



Valvata cristata Miill. 

 SphcBrium corneum I.. 

 Pisidium nitidum Jen. 



,, milium Held. 



There are evidently no river deposits as Ancyliis fluviatilis 

 and Nevitina fl^iviatilis are absent, and the conditions of life 

 when the deposits were laid down would seem to be similar 

 to those obtaining to-day, viz., a deep lake fed by springs, 

 with a shelving shore fringed with reed beds. 



Hale Moss is a small patch of a few acres, mostly white with 

 marl and litter, covered by shallow peat, occupying what was 

 the deepest (30 feet) hollow of the ancient Burton Lake. The 

 proportion of shells in the marl, here is very much less than in 

 that at Hawes Water. The following species occur in the marl, 

 and may be grouped thus : — 



Open Water. 



L. pereger Miill. 

 Valvata piscinalis Miill 



Marsh. 



L. truncatula Miill. 

 Pisid. pitsillum Gmelin 



Reed Belt. 



Valvata cristata Miill. 

 Pisidium nitidum Jen. 



,. cinereum Alder. ,, obtusale Pf. 



The noticeable fact here is the absence of the Planorbis 

 group and shallow water species — pointing to the existence of 

 a well-tilled lake of great dimensions, which has now entirely 

 disappeared. 



In the marl deposit, L. pereger far exceeds in number all 

 the other species. The shells are not lacustrine in form, but 

 are very similar to those of the Irish marls. In regard to this 

 deposit, Mr. A. S. Kennard says : ' Judging from 3'-our list, the 

 deposit is not a shallow water one, and was laid down in two 

 to three fathoms '....' Planorbis is a shallow water form, 



and not likely to occur in a deep water deposit.' 



' Bithynia tentaculata is rather a shallow water form, whilst 

 the hall-mark of shallow water is Linincca st agnails and Limncca 

 palustris.' 



As will be seen, Planorbis and Bithynia are absent, only 

 deep water species being found. 



Naturalist, 



