20 NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 



beau) to uniformly black (var. fiigrescens Colb.). The more striking 

 intermediate forms between these two extremes have also been 

 differentiated and described. 



The species has been found living in company with marine 

 shells in Loch Stennis (Orkney), the Baltic, and other places. 



Mr. J. MacGillivray (Zool., 1852, p. 3430) records that 

 some large water-pipes which had recently been taken up in 

 the City Road, London, to be replaced by others, were inhabited 

 by great numbers of Neritina fluvia tills , a Llmncea, &c. From 

 the state of the interior of the pipes they had evidently been 

 under ground for some years. The shells were in good con- 

 dition and coloured as usual. 



Mr. Warington states that he has noticed this species to 

 have the power of spinning a web or thread. Mr. G. S. Tye 

 says " its structure renders it impossible for it to spin an upward 

 thread, and the nature of its habitat alike precludes it, and as 

 it could not float in running water it could not therefore spin a 

 downward thread. The act of floating is not a normal one 

 with the creature, though it might perform it as mollusca some- 

 times do when placed under circumstances which allow of it, 

 and if it floated there is no reason why it should not spin a 

 downward thread." 



Its distribution in Yorkshire — as shewn by the records — 

 extends along a broad tract of somewhat level country from the 

 south-east to the north-west, being found in nine oUt of the 

 twenty-four districts into which we have divided the county. 



As yet three varieties only have been found in the county, 

 but doubtless others will reward the assiduous conchologist. 



It would be interesting to verify the following observations 

 on development, given by Mr. R. Tate, on the authority of 

 Clapar^de : — 



Each female deposits her egg-capsules in clusters of fifty 

 or sixty on the surface of the shell of her neighbour, and 



Trans. Y.N.U;, 1880 (pub. 1883). Series C 



