264 NELSON : ON THE LIMN^ID^. 



habitats and in this case the three species were evidently away 

 from home, their favourite habitats being small and shallow, in 

 fact nearly dry, ditches and grassy ponds. In searching these 

 ditches when dry in summer Planorbis spirorhis will be found 

 with a solid epiphragm waiting the return of rain. 



Crossing the bridge over the drain we saw a small grass- 

 grown pond in a field ; we pushed our way through the hedge, 

 and after some searching obtained a few examples of Planorbis 

 naittileus, the smallest and I think I may say the prettiest, of 

 the genus, having the whorls covered with small ridges, which are 

 in some cases produced into rather long and elegant spines ; 

 this latter form is called var. crista. 



Leaving the pond we regained the road and sat on the 

 trunk of a fallen tree, and whilst we partook of refreshment an 

 old man, a native of the district, accosted us, and during the 

 conversation stated that the whole district had been a large 

 common which was enclosed and drained somewhere about a 

 hundred years before. I mention this because I have an idea 

 that Limncza glabra is a species that is likely to die out or be- 

 come more rare as the old commons become drained and 

 destroyed. I have collected it in many districts, and have been 

 enabled in nearly every case to trace its connection with 

 commons by the survival of the plants usually met with in such 

 localities. 



Getting near to the village of Sandholme, which by-the-bye 

 has got a descriptive name, we come to a portion of the common 

 covered with small shallow grassy ponds, with here and there 

 holes where sand has been dug. iSie ponds seem to be ideal 

 habitations for mollusks, but with the exception of Limncea 

 peregra and Planorbis spirorbis, there seemed to be very little 

 in them, but in a small ditch that was almost dry we obtained 

 Planorbis spirorbis, Physa hypnorum and Limncza glabra. 



Just before we entered the village we came to a drain 

 which had not been cleaned out and which was consequently 

 full of various species of aquatic plants and an abundance of 



J.C, v., Jan., 1888. 



