NERITINA. 5 



variations of form and colour met with in foreign ex- 

 amples. These varieties have been elevated to the rank 

 of species by some of the continental couchologists. In 

 the recent monograph of the genus, by Mr. Sowerby, 

 the following are enumerated : zebrina, Pelojjonensis, Nu- 

 midica, Mittreana, Recluz ; thennaUs, Boubee ; intexta, 

 Villa ; Sardoa, irifasciata, Menke ; Hildreichii, Schwerz. 



The animal is whitish, with a black head and muzzle ; 

 the foot is more or less speckled with black ; the tentacles 

 are white, with a black line running along their length ; 

 the sus-tentacles bear rather small black eyes. The crea- 

 ture is shy of showing much of its body in walking, a 

 habit common to the marine as well as the fresh-water 

 species of this group. 



The Neritina lives in rivers having their outflow on 

 both the eastern and western sides of England. The 

 Thames, Trent, Ouse, and Humber, and their tributaries, 

 the Severn and Avon claim it among their inhabitants. 

 Mr. Jeftreys finds it at Swansea, and Mrs. Richard Smith 

 has collected it in Blenheim lake. Mr. Peach informs us 

 that he has taken it " once in Fowey harbour, and once 

 on Goran beach in Cornwall, on both occasions quite 

 fresh, and evidently derived from some of our fresh-water 

 streams." Captain Brown states that it is found in the 

 Tyne and Tweed, and Mr. Hogg mentions it as occur- 

 ring near Stockton ; but, according to Mr. Alder, the 

 Northumberland and Durham specimens have most pro- 

 bably been derived from ballast. Rare near Scarborough 

 (Bean). We have found it abundant, but dead, and 

 undoubtedly imported with ballast, on the shores of the 

 Firth of Forth in Fife, and doubt whether its Scottish 

 localities enumerated by Brown (Forth, Tay, and Clyde), 

 are not all of the same kind. Strange to say, however, 



