2l8 JOURNAL OF CONCHOLOGY. 



ON PLANORBIS DILATATUS, P. GLABER, AND 

 SPH^RIUM OVALE. 



By THOS. ROGERS. 



(Read before the Conchological Society.) 



In the summer of 1869 the American raoUusk Planorbis 

 dilatatus was discovered in a canal on the west side of Man- 

 chester, and in the autumn of the same year it was found in 

 another canal on the east side of Manchester— the two localities 

 being about five miles apart. In March of this year I sent 

 some of these specimens to Mr. Bates, of Burnley, and he im- 

 mediately wrote to say that he identified them with some shells 

 that he had collected in a water lodge at Burnley, and sent a 

 number for my inspection. The theory set up by Dr. Jeffreys 

 and m3'self, after examining both the Manchester localities, was 

 that it had been introduced by means of American cotton, as a 

 good deal of the refuse from the cotton cleaning machines of 

 the mills found its way into the canal where the shells were 

 found. I, myself, went a little further with this theory, and sur- 

 mised that the mollusk had been introduced during the cotton 

 famine, occasioned by the war of secession, and that the intro- 

 duction into these two localities were distinct and separate 

 introductions. A few years after its discovery in Manchester, 

 and when the canal was run dry for repairs, I saw in it count- 

 less numbers on the sides of the canal, extending about a mile 

 from where it was first found, and I ventured to predict at that 

 time that it would ultimately become a very common species \ 

 but unfortunately, nearly all these vast numbers were killed by 

 the men who " re-pointed " the joints of the bricks of the canal 

 waterway with mortar containing a good quantity of lime. It 

 is interesting to know that after a lapse of eighteen years the 

 mollusk has again been found abundantly at Burnley, and it is 

 also interesting to enquire if the theory first set up still holds 

 good. From enquiries I have made relative to the environment 

 of the lodge in which it is found and the habitat in which it 



J.C, v., July, 18S7. 



