33 



reader Xo figures 12 and 13, confining the delineation 

 to a few remarks only as to its form. 



Neritina fluviatilis is a fresh- water species. 



The shell is univalve. The spire possesses but a few 

 whorls, the last convolution being exceedingly large in 

 comparison to the others. The colour is variable, some 

 gpecimeos being nearly black, whilst others are red ; 

 this colonring is scattered over with elongated cream- 

 white spots. The specimens from the Lenton Canal 

 are green, with nearly black markings. 



Locality seems to have great influence on the colour 

 of a shell. It has invariably been noticed that the 

 specimens taken from the river Trent are much darker 

 than those obtained elsewhere in this neighbourhood, 

 probably owing to the depth, and more especially to 

 the rapidity of the stream. This remark applies equally 

 to other species besides Neritina fluviatilis, for Unio 

 tiimidus, Unio pictorum, Anodonta cygnea, Bithinia 

 tentaculata, and Cyclas rivicola procured in the river 

 Trent are all much darker than in any other locality in 

 the vicinity of Nottingham. This diff'ereDce in colour 

 is strikingly shown when specimens taken from the 

 Beeston Canal, near its junction with the river Trent, 

 are examined with the Trent shells, although within a 

 few yards of the same spot, and it is even more strik- 

 ingly seen from a comparison of shells procured from 

 the Trent near the mouth of the Soar with those taken 

 a few hundred yards higher up the Soar. 



In Neritina fluviatilis the aperture is obliquely semi- 

 oval, the interior being tinged with blueish-white, and 

 having a polished appearance. The colour of the oper- 

 culum is soaiev,-ha.i of an orange-yellow, having a nar- 

 row orange-scarlet band running round it, at nearly the 

 edge of the operculum. 



The dimensions of large specimens obtained from 



he Trent, near Beeston Ryelands, and from the canal 



