MEANS OF DISPERSAL 33 



be found in considerable numbers along the margins of 

 the river, clinging to limbs of trees and pieces of bark ; 

 vast numbers oi Pleiirocera suhdaris (which abounds in 

 the small lakes of the Bay Island, &c.);, he also states, 

 are to be found in July and August along the margins 

 of the river, clinging to drift-wood, having been carried 

 by a sudden rise in the waters from the different lakes 

 in the Bay/ Cooper's Creek, Central Australia, ac- 

 cording to Mr. E. B. Sanger, yields, amongst other 

 things, gastropods of three genera, ** Physa, Paludina, 

 and Tryonia!' which (he believes) die when the water 

 dries up ; each flood, however, is found to stock the 

 creek again by bringing down young ones, which, it is 

 important to notice, are actually to be seen, "in all 

 stages of growth, in the flood-water." " As showing 

 that Unionidce are carried over land by floods, Mr. 

 C. T. Simpson instances the finding of a Unio in great 

 numbers in low places and drains in the piney woods 

 of South Florida, at quite a distance from any stream, 

 where not a drop of water is to be seen outside, perhaps, 

 of three months of the rainy season, and where, during 

 the remaining nine months of the year, the animals 

 must have lain dormant in slightly damp sand ; he had 

 dug them out in such places during the dry season by 

 the bushel.^ Similarly, Mr. Cuming is said to have 

 collected living specimens of Cyclas maculata while 



^ W. A. Marsh, " Conchologists' Exchange," ii. (1887-8), 81, 

 103. 

 ' E. B. Sanger, "American Nat.," xvii. (1883), 11S4-5. 

 3 C. T. Simpson, "Nautilus," v. (1891), 16. 



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