326 



NOTES ON 

 THE MOLLUSCA OF THE VALLEY OF THE COLNE. 



By J. E. COOPER and A. LOYDELL. 



(Read before the Society, Fel.i. loth, 1909). 



In working out the census of Middlesex shells we have been struck 

 by the abundance and variety of mollusca in the Colne Valley. 



At Harefield, which is the first village in the north-west of the 

 county, is the only patch of chalk in Middlesex. Although it only 

 covers about one square mile, it has afforded six county records, 

 besides several species which are uncommon elsewhere. In or near 

 the chalk-pits are to be found Arion subfiisciis, Fyramidula rotiindata 

 var. rufuia, Vitrina peliucida, Vallonia cosiata, V. excentn'ca, Helicella 

 virgata, H. caperata^ Helicigona arbustorum, Jainitiia muscortim, and 

 Po matins elegaus. In a wood near by we have taken Acanthinula 

 aculeata, Punctuin pyg/ineian, and Euconuhis fidvus on dead holly 

 leaves. Eight species of Vitrea occur here. There is a fine colony 

 of V. scharffi by the river-bank, in which all the animals arc blue, 

 with large thin shells. A smaller colony in the great chalk-pit has 

 thicker shells with rather darker animals. The latter might be taken 

 for V. lucida from their external appearance, but from an examination 

 of the radula we refer them to V. scharffi. 



The river at Harefield is not very productive, but the ditches and 

 backwaters (more particularly those towards Denham Lock) yield a 

 considerable number of freshwater species. We have obtained five 

 species of Pisidium here, viz. : — P. ainnicum, P. subtni?icatui/i, P. 

 pulihellui/i, P. obtiisale, and P. gassiesianum. Our total for Hare- 

 field and neighbourhood (Middlesex portion only) is 65 species. 



Following the Colne for a few miles we reach Uxbridge. Here 

 the land shells are not so much in evidence. Spliyradiuni edentuluin 

 used to live in a copse which was destroyed when the new railway 

 line was built. Unfortunately, we have not yet discovered another 

 Middlesex locality for this species. Freshwater shells are abundant. 

 In the stream called Frayswater, or Frays River, are fine Limncea 

 auricularia, also Pisidium henslowiatium. A small piece of marsh 

 contains a flourishing colony of Paludestrina Jc/ikinsi and Pisidium 

 casertanum. In a ditch near we have taken Valvata cristata — rather 

 a scarce shell in Middlesex. In Uxbridge Marsh we have met with 

 small examples of Vivipara coniecta. 



Following the canal south, we come next to Yiewsley. Just where 

 the Slough branch canal crosses the Colne, there is a prolific little 

 marsh. Hygromia granulata and Zoiiitoides nitidus are abundant. 



