JOURNAL OF CONCHOLOGY. 417 



BIOLOGY OF SPHyERIUM CORNEUM. 



By HENRY CROWTHER, F.R.M.S. ' 

 (Curator of the Leeds Museum). 



(Read before the Conchological Society, with microscopical demonstrations, 

 March 14th and April 4th, 1894). 



This bivalved mollusc is common in that portion of the Leeds 

 and Liverpool Canal which runs through the western side of 

 Leeds, especially between the forges, into which hot water is 

 continually being discharged from condensers and twyers and 

 is aerated by opening lock-gates and over-flow goits. 



These little pelecypods present many points of interest. 

 I offer one or two for consideration. If put into a tall glass 

 vessel of water they will be seen to travel up its sides, with ease, 

 by the alternate expansion and contraction of the foot which 

 each possesses. An animal in a shell half-an-inch in length 

 crawled one inch in four minutes, lifting its shell three-eighths- 

 of-an-inch at each contraction. At various heights on the sides 

 of the vessel the molluscs anchor themselves by means of 

 molluscan threads, often several in number, which appear as 

 mucous prolongations of the mantle, and are dirty-looking from 

 entangled organic matter, desmids, and other algal cells. As the 

 animals seek higher levels they come to the surface film of the 

 water and there anchor, depressions in the film due to their 

 suspension being easily seen even without a lens. A sharp 

 knock on the glass causes film-suspended animals to fall through 

 the water to the bottom of the vessel, but as many catch and 

 hang on intervening weeds and even on the sides of the vessel 

 as they fall the threads are probably left trailing outside the 

 closed shell of the alarmed mollusc. 



A sprig of water thyme {Elodea) in the jar is soon peopled, 

 mostly by dropping surface-film specimens, and suspension soon 

 follows. It seems so strange to see these molluscs in such a 

 hurry to reverse the usual order of things, since in crawling 



