ROGERS: ON PLANORBIS DILATATUS, ETC. 219 



lives at Burnley, the argument is not conclusive. At the time 

 of its discovery at Burnley I enquired if there was a canal, and, 

 if so, were there any spinning mills ; the answer was that there 

 was a canal about a furlong off and there had been a mill, but 

 it had been burned down. I suggested, too, at the time, that 

 the canal in the vicinity of a cotton mill, on or near its banks, 

 should be examined, and a few days ago I received a letter 

 from Mr. Bates announcing that they had found it in thousands 

 near a cotton mill on the canal banks, but I do not know all the 

 particulars of this locality. It is rather singular that in all the 

 localities, both at Burnley and Manchester, that there are three 

 identical associations. First, that it is found amongst a green 

 algae, which I take to be the same species in each case. Second, 

 that there is an abundance of a form of Plumatella repens, which 

 Prof. AUman describes as a somewhat unusual form, and that 

 it is found in water artificially higher in temperature through 

 the discharge of water from condensing engines. I expressed 

 my opinion to Dr. Jeffreys at the time it was first found, that 

 the Planorbis lived upon the decaying substance of this 

 Plumatella and other Hydroid Zoophytes. Mr. Bates also in- 

 forms me that Mr. Long discovered Planorbis glaber along with 

 P. dilatatus in the same water lodge at Burnley — might we not 

 ask ourselves, although P. glaber is a well established British 

 species, whether the form of P. glaber found along with the 

 P. dilatatus may not be introduced American P. parvus 1 May 

 I say, in conclusion, that many persons express a doubt that 

 the vitality of the Planorbis would not sustain it during a voy- 

 age from America to England, and the subsequent passage 

 through a blowing machine. Dr. Jeffreys expressed himself 

 that it was no difficulty with him to accept this part of the 

 theory, and from examinations made of the waste from cotton 

 blowing machines by myself, I can readily believe that the shells 

 could pass through undamaged. I think too that this last 

 Burnley habitat is a direct American introduction, about the 

 same time as the introduction in Manchester. 



