14 THE DISPERSAL OF SHELLS. 



SpJicBriiivi corneinn^ Planorbis cariiiaius, Linincsa stag- 

 nalis, and Ancyhis lacustris ; while the smaller one, 

 about thirteen yards distant, contains Sphcerium 

 corneuin^ Planorbis carina ttis^ Limncea stagnalis^ and 

 Limncea trimcaUila ; and some idea of their individual 

 abundance may be gathered from the following note 

 of four caddis-cases — selected from a number col- 

 lected in both ponds — bearing, together, no less 

 than forty-five shells, (i) Five shells attached, two 

 of Sphieriuvi, one of Limncea^ and two of Ancylus ; 

 (2) ten shells attached, eight of Splia^rium, one of 

 Pla7iorhis, and one of Limncea; (3) fourteen shells 

 attached, eleven of SpJiceriuni^ one of Planorbis, and 

 two of Limncea ; (4) sixteen shells attached, one of 

 Sphcerium i and fifteen of Pla7iorbis} 



Pond near the Black Hills, Leeds. — During a period 

 extending over some twenty-four years Mr. W. Nelson 

 has obtained Sphcerimn lacustre, Pisidium pusillum^ 

 Planorbis natitileus^ Planorbis vortex^ Planorbis carina- 

 tus, Planorbis corneiis, Planorbis cojitortus, Physa fon- 

 tinaliSy Limncea peregra^ Limncea stagnalis, and Ancylus 

 lacustris from this pond, which is of small size, isolated, 

 as Mr. Taylor assures me, from other water, and with no 

 inlet except "a natural drainage from the field. '^ In 

 times of heavy rain there is an overflow of surplus 

 water, but this disappears in or spreads over the land 



* Mr. J. W. Taylor, of Leeds, has obligingly looked over the 

 shells from these ponds and those at Welton-le-Wold, Tothby, 

 and Rigsby, determining the Pisidia, and confirming my naming 

 of the other kinds. 



