302 CONCHIFERA. 



be " probably the Mytilus polymorphus Gmelin, 3363, 

 which is found in abundance, attached to shells and 

 timber, in the Commercial Docks, by James Bryant, 

 Esq., who uses the animal as bait for perch." Mr. 

 Sowerby observes, that "the strong resemblance 

 which it bears to the marine Mytili is very remark- 

 able. Independently, however, of the septa within 

 the valves, there are many other differences to be ob- 

 served, several of which are in the structure of the 

 included animal, although it possesses a strong byssus ; 

 among others, the foot is small and the lips of the 

 mouth are differently placed, being more like those in 

 the animal of the Unio ovalis. It has two tubes, and 

 the mantle is united almost all round, and bordered 

 with a bright orange between two bands of black. 

 Some of the septa within the beaks appear to be a 

 kind of disease, as they are not constant." 



" The same species is found in the Danube and in 

 the rivers of Russia; but the British species are much 

 larger and finer than any foreign one I have seen." 

 (Linn. Trans, xiv. 585.) 



In 1825, in a List of Shells not taken notice of 

 by Lamarck (Ann. Phil. 1825), I stated that this 

 shell would " perhaps form a genus distinct from 

 MytUus, and peculiar for its fresh- water habitation," 

 and added that, " like Mollusca of that station, the 

 animal can live for a long time out of water. I have 

 kept one for three weeks, when it was still healthy. 

 It is found in the Commercial Docks, where it most 

 likely has been introduced with timber from the 

 Volga." 



I am now confirmed in the idea that this is the 

 way in which they were introduced, as a friend has 



