34 



near the Wollaton Park wall, are — in length five- 

 twelfths of an inch, and in breadth three and a half 

 twelfths of an inch. 



In the month of September, the large stones which 

 are under water in the Trent are covered over with the 

 young Neritina fluviatilis. At first they seem liiie so 

 many cheese-mites dispersed over the stones, apparently 

 immovable, and glued to the respective spots which 

 they occupy. They are of a yellowish-white colour, 

 and, when rather more advanced, change to brown with 

 faintly-perceptible yellow markings. On attaining 

 about double the size of a cheese-mite they move about. 

 At this period, excepting being very fragile, they have 

 a similar character to the parent shell. Stones which 

 were buried about ten or twelve inches under water 

 were most crowded with the young of Neritina fluvia- 

 tilis; however, others dredged from a depth of ten feet 

 contained many specimens. 



Neritina fluviatilis was first described by Dr. Lister, 

 in 1678. 



This shell frequently has a calcereous incrustation 

 deposited by the water over the external surface, and 

 this covering gives the appearance of pieces of dirt, by 

 which means these muUusca frequently escape being 

 attacked by fish and water fowl, who mistake them for 

 dirt. 



The Neritina fluviatilis may be classed amongst our 

 very local shells, being everywhere coufiued to certain 

 limits. The localities in this part of the county are, 

 the river Trent, near Beeston Ryelands (where it is 

 quite abundant) ; the river Soar, at Tbrumpton ; the 

 canal near Beeston (in which it is rare, and may have 

 been carried into it from the Trent) ; and the canal be- 

 tween Lenton and Radford. Mr. Winstanley has aiso 

 dredged it from the Trent, below the bridge at 

 Nottingham. 



