Extracts from the Minute-Book of the Linnean Society. 585 
Nov. 2. 
Nov. 16. 
proving that these insects, which have been hitherto 
considered as distinct species, are the sexes of the 
same, P. Polycaon being the male. ‘This interesting 
specimen is from Brazil, and was sent to Mr. Mac- 
Leay by John Dixon, Esq., of Rio de Janeiro. 
Mr. James De Carle Sowerby, F.L.S., presented 
specimens of a Fresh-water Shell, probably the Myti- 
lus polymorphus, Gmel. 3363, which is found in abun- 
dance, 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 remarkable. Independently, however, of the 
septa within the valves, there are many other diffe- 
rences 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 band of 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 con- 
stant. The same species is found in the Danube, and 
in the rivers of Russia; but the British specimens 
are much larger and finer than any foreign ones I have 
seen.” 
Read a Letter from Mr. John Atkinson of Leeds, 
F.L.S., accompanied with some specimens of Cole- 
opterous Insects which were discovered among the 
linen 
