320 OBSERVATIONS ON MOLLUSKS. 



Even supposing that the spawn had been dormant in 

 the soil, or conveyed there in any way the imagina- 

 tion can suggest, still how could the shells have 

 acquired so rapid a growth in the short time the 

 water had been standing in that spot ? The puddle 

 was scarcely more than three feet by two across ; it 

 had not been in existence above a fortnight at long- 

 est ; it was only a few inches deep ; and half a 

 dozen fine days would have been sufficient to lay it 

 dry again. Such, in fact, proved to be the case 

 before the month had expired, and the species has 

 not been observed since in that locality. 



Professor Henslow has communicated to me the 

 following case of a mollusk being found in plenty in 

 rather a singular situation, and in which also, as in 

 the case last-mentioned it is not very easy at first 

 sight to account for its appearance, though the conjec- 

 ture he has offered is perhaps the most probable one. 



" The Messrs. Ransome, at Ipswich, supply water 

 to a trough, connected with the supply of a power- 

 ful steam-engine, which is obtained by a bore of 

 considerable depth through the chalk. After sus- 

 taining a temperature of about 100, this water is 

 pumped into a large cistern upon the roof of their 

 establishment, where it retains a temperature of 

 about 70 degrees. This tank is regularly cleaned 

 out once a year. My attention was directed to the 

 fact of its being continually replenished with a very 

 large number of the Limneus pereger. Individuals of 

 small dimensions (when I inspected the tank) were 



