Dr. Tate on the Mollusca of Alnwick. Ill 



The richest localities are those where limestone occurs, as 

 at Ratcheugh Crag and the Calish woods, this rock furnish- 

 ing the lime of which the external covering of the mollusca 

 is for the most part composed. Particular plants, moreover, 

 afford a resting place to many species. Equisetums and 

 grasses, which contain a large per centage of earthy salts, are 

 much frequented by land shells. Many mollusca, in the same 

 way as plants, are found in every situation and on every variety 

 of soil, while others again affect particular habitats. 



The geological peculiarity of a district influences the dis- 

 tribution of land shells much more, in England at least, than 

 geographical position. All of the forms found near Alnwick 

 are, with one exception, {Helix lamellata), observed in 

 Hampshire, at the opposite extremity of the country. Those 

 peculiar to this southern part of England, and which are not 

 observed in the north, flourish on a cretaceous soil ; among 

 those may be enumerated, Cyclostoma elegans, Bulimus 

 acutus and Helix cantiana. 



The fact that mollusca pass a large portion of their time in 

 winter in a state of hybernation, when the influence of climatal 

 peculiarity is scarcely felt, accounts perhaps for the absence 

 of any striking difference in the fauna of two opposite extre- 

 mities of this country. 



MOLLUSCA. 

 Class I. — Gtasteropgda. 

 Ord. — Pneumonobranchiata. 



FaM. HELICIDiE. 



Genus — Vttrina, Drap. 



1. V. pellucida, Miill. 



Common under stones, among moss and decaying leaves. 

 Ratcheugh, Hulne, Rugley woods, &c. Live speci- 

 mens are most frequently met with after a shower of 

 rain and in damp weather. 



Gen. Zonites, Gray. 

 The species of this difficult genus are not easily distinguish- 

 able ; but having carefully examined a considerable number 

 of specimens, I venture to give specific descriptions from my 

 own observations, in the hope of facilitating the determination 

 of the species. 



2. Z. cellarius, Miill. 



One of our common shells. Beneath stones, about old 

 walls, among grass in woods, fields, and occasionally 

 in damp cellars. Ratcheugh, &c. Shell flattened with 



