856 ISLAND LIFE 



Land and Freshwater Shells. — In the first edition of this 

 work four species were noted as being, so far as was then 

 known, exclusively British. One of these, Cyclas 'pisi- 

 dioides (now called Sjyha^ri'itm pisidioidcs) has been dis- 

 covered on the continent, but the other three remain still 

 apparently confined to these islands ; and to these another 

 has been added by the discovery of a new species of 

 Hydrobia in the estuary of the Thames. The peculiar 

 species now stand as follows : — 



1. Geomalacus MACULOsrs. — A beautiful sing, black spotted vnili 

 yellow or white, found on rocks on the sliores of Lake Caragh in Kerry. 

 It was discovered in 1842, and has recently been found also at Glengarriff 

 in Cork. An allied species is found in France and Portugal. 



2. LiMNEA INVOLUTA. — A pond snail Avith a small polished amber- 

 coloured sliell found only in a small alpine lake, and its inflowing stream 

 on Cromagloun mountain near the lakes of Killarney. It was discovered 

 in 1838, and has frequently been obtained since in the same locality. It 

 is sometimes clas:;ed as a variety of Limnca pcregra, and is at all events 

 closely allied to that species. 



3. Hydrobia jenkinsii. — A small shell of the family Rissoidoe inhabit- 

 ing the Thames estuary both in Essex and Kent. It was discovered only 

 a few years ago, and was first described in 1889. 



4. AssiMiNEA cjrayana. — A small estuarine pulmonobranch found on 

 the banks of the Thames between Greenwich and Gravesend, on mutl at 

 the roots of aquatic plants. It has been discovered more than sixty years. 



But besides the above-named species there are a con- 

 siderable number of well-marked varieties of shells which 

 seem to be peculiar to our islands. A list of these has 

 been kindly furnished me by Mr. Theo. D. A. Cockerell, 

 who has paid much attention to the subject ; and after 

 omitting all those whose peculiarities are very slight or 

 whose absence from the continent is doubtful, there remain 

 a series of forms some of which are in all ])robability really 

 endemic with us. This is the more j^robable from the fact 

 that an introduced colony of Helix nemoralis at Lexington, 

 Virginia, presents numerous varieties among which are 

 several which do not occur in Europe.^ The following list 

 is therefore given in the hope that it may be useful in 

 calling attention to those varieties which are not yet posi- 

 tively known to occur elsewhere than in our islands, and 



^ See "The Virginia Colony of Helix nemoralis," T. D. A. Cockerell. 

 in The Nautilus, Vol. III. No. 7, p. 73. 



