^go YorksJiire Naturalis/s at CaKiJionic. 



including Arioii intoincdiiis several species of Vitna, Hygromia 

 hispida, Helix Iwiioisis and Clausila hidentata. In the canal at 

 Barugh several fresh-water species were noted, including 

 Liniiiaca stagiialis, L. aiiriciilaria, Planorhis carinatus P. con- 

 torfiis, Wilrafa piscijiaMs, Bithynia tentaculata and Paludestrina 

 jenkiiisi. In a pond near Cawthorne were Planorhis albus, 

 with PisidiiiDi piisillum and its var. grandis. 



In the Lake at Cannon Hall Park dead shells of Limnaea 

 miricidavia, L. peregev, Anodonta cygnaea and Unio pictorum 

 were found ; in one of these a crayfish had made its home. 



Deffer and Cawthorne Park Woods proved rather unpro- 

 ductive. Eiiconuliis fidvus and Vitria crystallina in the former, 

 and Avion siibfuscus in the latter were all that were noted. 

 On the roadside near Kexbro Helix horiensis was found in some 

 variety, lilaci^ia being the most notable. The dryness of the 

 weather in some degree accounted for the shortness of the list 

 of land shells. Paludestrina jenkinsi was first found by the 

 writer on May 22nd of this year when some members of the 

 section paid a visit to the district. This species was first dis- 

 covered at Plumstead in 1889 by Mr. A. J. Jenkins, and has 

 since been found in many parts of this country, sometimes (as 

 in the present instance) in incredible numbers. How it is 

 that it suddenly appears in such numbers and in such widely 

 distinct places is one of the problems that has not yet been 

 satisfactorily solved. One suggestion is that it is introduced in 

 timber from the Baltic, which may be very likely in this in- 

 stance as large numbers of pit props must be imported into the 

 district every year, though this particular part of the canal has 

 not, I believe, been used for traffic for over twenty years, and 

 it seems unlikely to have been overlooked by such energetic 

 conchologists as Wilcox, Hebden and Whitwam, who must 

 have worked the district many times. 



Another suggestion is that this species has cycles of abun- 

 dance, sometimes appearing in large numbers in one year and 

 then in gradually decreasing numbers (as in the Spen Valley 

 instance), till conditions favourable for another revival occur, 

 and that many of the older conchologists either overlooked 

 them altogether, or mistook them for the young of larger 

 species. 



The following is a complete list of the mollusca noted during 

 the excursion: — 



Naturalist, 



