l6 ■ THE DISPERSAL OF SHELLS. 



interesting and curious and is certainly worth giving,' 

 but I do not put it forward as of so much value for 

 us as some of those previously referred to (the dew- 

 ponds of the South Downs for instance), for I do not 

 think it seems so clearly to imply the existence of dis- 

 persal independently of man ; on the Downs, day after 

 day, as Mr. Reid states, " one meets only the shepherd 

 tending the sheep, or the farmer making a short cut 

 across the open country," and everything seems to 

 show that shells are not likely to have been carried 

 to the dew-ponds by human agency, but in Leeds, 

 on the other hand, quite a number of shell collectors 

 have resided for many years past, and it seems just 

 possible that someone, having collected a number of 

 molluscs for which he had no particular use, may have 

 thrown them into the pond in question, but this, of 

 course, is very unlikely ; it seems just possible, also, 

 I venture to think, that the conchologists who col- 

 lected there during the earlier years may have uncon- 

 sciously introduced some of the species adhering (per- 

 haps when very minute) to their scoops or collecting 

 nets, and it is at least noteworthy that Planorbes^ 

 so conspicuous among the additions, commonly thus 

 adhere. 



The presence of Limncea humilis, " by the hundreds," 

 in a small artificial pond, fed by a windmill from a 

 well twenty feet deep, was noted in the West American 

 Scientist during 1885 ; the pond, situate in the vicinity 

 of Todos Santos Bay, Lower California, was only about 

 ten years old, a i^w inches deep, and about six feet 



