126 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



Besides this species of Planorbis, I have got other 

 four near Rothesay, viz. : P. nautileus (L.), from 

 marshy ground by the side of Loch Ascog ; P. albus 

 (Mull.), from Greenan Loch, Loch Fad, and Loch 

 Ascog; P. contortus (L.), from Loch Fad, where it 

 is a common species ; and P. spirorbis (Mull.), from 

 a little loch or dam on the hill immediately above 

 the quarry at Ascog, on the south side of Ascog 

 Burn. 



Vertigo antivertigo (Drap.). — This species has been 

 previously recorded as occurring in Bute and also 

 in Arran.* The specimens now exhibited were found, 

 along with one or two more of the same species, 

 in a somewhat marshy hollow by the side of Loch 

 Ascog, on the 10th of last month. To judge from 

 the few records of its occurrence, it appears to be 

 one of the rarer species of this genus occurring in 

 Scotland. 



Pisidium nitidum, Jenyns. — I find this species in all 

 the lochs already mentioned, and it is not rare in 

 any of them. 



Pisidium jmsillum (Gmelin) and P. fontinale (Drap.) 

 are also found near Rothesay — the first occurring 

 at Loch Ascog and Greenan Loch, and the second 

 in Loch Fad. 



The Pisidia are a rather difficult group to work 

 up, owing to the obscurity of the specific characters, 

 and to "their great tendency to variation through 

 being readily reacted on by their surroundings. 

 There is no "way of getting over the difficulty but 

 by the examination and comparison of large num- 

 bers of specimens. Referring to his investigation of 

 this group, Dr. Jeffreys says: "My own cabinet 

 contains no less than 274 parcels of Pisidia, which 

 have been, in the course of the last thirty or forty 

 years, collected from different localities and sources, 

 and comprise many thousands of specimens. . . . 

 I have collected these tiny shells in many parts of 



•Fawna and Flora of the West of Scotland., p. 42. 



