48 SINGULAR HABITAT UNDERGROUND SNAILS chap. 



could not have been washed into the streets from any adjacent 

 river or pond, and their true origin was probably indicated 

 when it was found that the funnel-shaped cloud which burst 

 over the town had passed across the one piece of water near 

 Paderborn, which was known to contain the Anodonta in 

 abundance. 



Cases of Singular Habitat. — Mollusca sometimes accustom 

 themselves to living in very strange localities, besides the 

 extremes of heat and cold mentioned above (pp. 23-24). In the 

 year 1852, when some large waterpipes in the City Eoad, near 

 St. Luke's Hospital, were being taken up for repairs, they were 

 found to be inhabited in considerable numbers by Neritinct 

 fiuviatilis and a species of Limnaea? Breissensia polymorph a 

 has been found in a similar situation in Oxford Street, and also 

 in Hamburg, and has even been known to block the pipes and 

 cisterns of private houses. In an engine cistern at Burnley, 

 60 feet above the canal from which the water was pumped 

 into the cistern, were found the following species : Sphaerium 

 corneum, S. lacustre ; Valvata piscinalis, Bithynia tentaculata ; 

 Zimnaea peregra, very like Succinea in form and texture ; 

 Flanorhis alhus, P. corneus, P. nitidus, P. glaber, and thousands 

 of P. dilatatus, much larger than the forms in the canal below, 

 a fact probably due to the equable temperature of the water in 

 the cistern all the year round.^ In certain parts of southern 

 Algeria the fresh-water genera Melania and Melanopsis inhabit 

 abundantly waters so surcharged with salt that the marine 

 Cardium edule has actually become extinct from excess of brine. 

 The common Mytilus edulis is sometimes found within the 

 branchial chamber and attached to the abdomen of crabs 

 (Oarcinus maenas), which are obliged to carry about a burden 

 of which they are powerless to rid themselves (see p. 78). A 

 variety of the common Limnaea peregra lives in the hot water 

 of some of the geysers of Iceland, and has accordingly been 

 named geisericola. 



Underground Snails. — Not only do many of the land Mollusca 

 aestivate, or hibernate, as the case may be, beneath the surface of 

 the soil, but a certain number of species live permanently under- 

 ground, like the mole, and scarcely ever appear in the light of 

 day. Our own little Caecilianella acicula lives habitually from 



1 Zoolu'jlst, X. p. 3430. - Science Gossip, 1S8S, p. 2SL 



