134 REPORT— 1839. 



three Helices, one Bulimus, two Achatinas, two Clausiliae, one 

 Balea, five Pupas, one Carychium, ten Planorbes, two Physag, 

 six Limnei, and two Ancyli. Of these, twenty-two species 

 are generally distributed throughout the county ; eighteen are 

 local, found at a few places only, and those not fenny ; seven 

 are local species, having fenny localities, and nineteen are spe- 

 cies found almost exclusively in the fen districts. Of the ter- 

 restrial species thirty-three frequent woods, gardens, hedges, 

 and bushy places ; four are found on heaths, dry banks, and 

 open places ; six in fenny districts, and one in cellars and 

 damp buildings. Of the aquatic species seventeen are found 

 in fens and low ponds, and four are not confined to the fens. 

 Associated with these Pulmonifera, are one Cyclostoma, one 

 Neritina (which is confined to the river Cam), two Valvatae, 

 three Paludinse, one Anodon, one Unio, three species of 

 Cyclas, and six species of Pisidium. In the list of Pulmo- 

 nifera is also included with a query the Physa alba, of which 

 Mr. Jenyns says he received a single specimen exactly accord- 

 ing with Turton's figure, from a deep drain in the heart of the 

 fens. " It was given me by a gentleman who was formerly 

 resident in the neighbourhood of the spot, and who observed 

 it with many others that had been thrown out with the mud 

 on the occasion of the drain being cleaned. Not aware at the 

 time of its being anything peculiar, only two or three spe- 

 cimens were brought away. I rather think the drain is 

 now filled up." Such accidents well deserve our attention, 

 frequently causing the destruction of perhaps the only locality 

 in a district of some rare aquatic species. There are certain 

 species, such as the Irish Limneus involutus, which are only 

 known in one or two limited localities. An accident, such as 

 that which destroyed this Physa, might render such local forms 

 altogether extinct ; and should it have been the fate of any 

 such extirpated species to have remained unrecorded, in case 

 it afterwards occurred fossil in a bed of fresh-water marl, a 

 dangerous geological fallacy would take place. Mr. Jenyns 

 notes another instance of the disappearance of an aquatic spe- 

 cies. Of Limneus glutinosus he writes, " Some years back 

 this species occurred in the utmost profusion in one marshy 

 spot not a mile from my house ; but it has since disappeared, 

 and I never observed it in any other locality." 



District III. — Throughout a great part of the third or south- 

 western English district the negative influence of structure is 

 very evident, most especially in that portion of it where cli- 

 mate should exhibit its influence most forcibly, namely, the 

 counties of Cornwall and Devonshire. In these counties the 



