DREISSENA. 
261 
morpha. Cantr, Ann. Sci. Nat. vii. 308. — Tichogonia 
Chemnitzii. Rossm.lcon.i. 1113. t. 3. f. 69. — Dreissena 
polymorpha. Van Beneden^ Ann. Sci, Nat. 1835, 210. t. 8. 
f. 1 — 11.; 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 Linnsean Society, stating them 
to 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 
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.) 
