414 Quarterly Journal of Concliology. 



Having kept nearly every British species of the Limn?eidte in 

 confinement on purpose to observe their habit of spinning, and 

 not having seen some species use this means of locomotion at all, 

 others seldom, and some often ; some when young but less often 

 as they grow older, and others all their lifetime, I have been led 

 to advance a theory whereby to account for this varied use of 

 these threads. To this end I have drawn up the following table. 

 While writing it, I am sensible of its imperfections ; but if it only 

 serves as a nucleus to stimulate other observers of the economy 

 of these creatures to frame a more perfect one, I shall be the more 

 satisfied with my attempt. 



Doubtless all the Liuinc^idiC are more or less experts in the 

 use of the thread, and in the pellucid stillness of their own domain, 

 when the eye of man is not present to pry into their daily avoca- 

 tions, this beautiful and delicate method of travelling is often used 

 by them. 



Planorhis Iineatus.\ — Inhabiting streams; could not spin a 

 thread in its native habitat. I have not succeeded in keeping it 

 alive long. 



Planorhis nltlJus,] P. nautlleus,^ P. alius, f P. glaber,\ P. 

 vortex,^ P. spirorbis,'^ P. contortus* Linnum truncal ula.\ — Of 

 these species some spend their lives on vegetation near the surface 

 of ponds or pools, and others inhabit shallow ponds or ditches, 

 which sometimes become dry in summer ; hence the necessity for 

 using a thread does not often occur. 



Planorhis ca/inatus,^ P. coniplanatus* — Living in the larger 

 ponds and pools where the water is of considerable depth, this 

 capability of thread-spinning often serves them to good purpose. 



PJiysa hypnoruni,* P. fontinalis^'^ Limnoia glabra-'^ — Inhabit- 

 ing deep ditches, ponds, or pools, and fond of indulging in sub- 



* Species I have seen spin a thread. 



•'r Species I have kept, but not seen spin, 



1 Species seen to spin by others. 



