DKEISSENA. 261 



morpha. Cantr. Ann. Sci. Nat vii. 308. Tichogonia 

 Chemnitzii. Rossm. Icon. i. 1113. t. 3. f. 69. Dreissena 

 polymorpha. Van Beneden, Ann. Sci. Nat. 1835, 210. t. 8. 

 f. 111.; Strickland, Mag. Nat. Hist. 1838, 361.; Moq. 

 Tand. Moll. Franc, ii. 598. t. 54. ; Forbes and Hanley, 

 B. M. ii. 165. t. 42. f. 4, 5., t. 2. f. 4. 



Inhab. lakes and rivers, attached to stones, timber, 

 and other shells. 



The fact of this animal having been introduced was 

 first brought before the public on Nov. 2. 1824, by 

 Mr. James de Carle Sowerby, when he presented 

 some specimens to the Linnaean Society, stating them 

 to be ( e 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 

 observed, 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.) 



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