28 Mr. Alder- s Catalogue of Land and Fresh water Shells. 



the Rev. R. Sheppakd's list of Suffolk shells, in the Linncean Society's 

 Transactions, contains 70 species — 36 land, and 34 fresh-water. In the 

 list now given for the vicinity of Newcastle, there are 71 species, of 

 which 45 are land, and 26 fresh-water. It would thus appear that, while 

 in the low lands of the southern counties the relative ^proportions of 

 these subdivisions are nearly equal, in the more elevated tracts of the 

 north they differ nearly as 2 to 1. 



It may be thought by some that, by attending to minute distinctions, 

 too many species have been introduced into the following Catalogue. 

 It is well known, however, to every observer of nature how very small 

 are the gradations by which species are often divided from each other, 

 especially in the lower classes of animals, whose organisation, being 

 more simple, affords fewer characters for specific distinction. Minute 

 characters too, are seldom detected on a general survey, and thus in 

 the progress of scientific inquiry, allied species are often confounded 

 at first, which, on a more intimate acquaintance, it is found necessary 

 to divide. Premising thus much, I submit the views of particular spe- 

 cies here taken to the judgment of those most conversant with the sub- 

 ject, having at the same time the satisfaction of knowing that they 

 are not without support from the opinions of some of our most eminent 

 British Conchologists. 



The habitats and localities here given, except in one or two instances 

 that are mentioned, must be understood to rest upon the authority of 

 my personal observation. My thanks, however, are due to my friends, 

 Mr. Albany Hancock and Mr. John Thornhill, for the communica- 

 tion of many habitats, observed during their active investigation of this 

 as well as other branches of the natural history of this neighbourhood. 



