132 PHILOSOPHICAL TKANSACTION8. [aNNO 1771. 



inches ; on the south-west side, 8 feet 6 inches ; and on the south-east side, 10 

 feet above the ground; it is all open southward for 25 yards; the north side is an 

 orchard, but no tree hangs over it. 



The latitude of Mr. Neal's house, at the south end of St. Martin's, adjoining 

 to Stamford in Lincolnshire, as taken by Mr. Edward Lawrence, in 1736, is 

 52° 39' 0". St. Mary's, the middle of Stamford, is half a mile farther north, 

 therefore its latitude is 52° 39' 30'. 



JCXIX. Observations on some Bivalve Insects,* found in common Water. By 

 Mr. Muller, of the new Acad, of Sciences in Bavaria, &c. p. 230. 



The name of bivalve is given only to those shell-fish, whose houses are com- 

 posed of 2 parts, such as muscles and oysters. Few of these are to be met with 

 in fresh water ; whereas a vast number are inhabitants of the sea. Mr. M. was 

 acquainted with no more than 4 different species, like the sea bivalve ; they are 

 found in the waters of Fridericksdal, near Copenhagen, and among them, one 

 has hitherto escaped the researches of conchiliogists. 



In return, nature has liberally stocked the same waters with small insects, 

 much more perfect than the inhabitants of the sea-shells, and likewise provided 

 with a double shell. It is sufficiently known, that muscles and oysters are ani- 

 mals extremely simple; since they want several of the more perfect organs, and 

 consequently enjoy life in an incomplete manner. The want of eyes, arms, legs, 

 &c. obliges them to lead an idle life, deprived of all the advantages which arise 

 from sight and motion. Nature, from which they received an habitation suffi- 

 cient to protect them from external injuries, seems to have fixed for life their 

 abode to one dark spot. Our bivalve insects, on the contrary, by opening their 

 two folding gates, enjoy both sight and motion, alternately dipping in the mud, 

 and darting through their element the water ; whenever they meet with bad com- 



• The Linnxan genus Monoculus, to which the insects described with too tnuch minuteness in 

 this paper, belong, is of great extent, and the species differ so much in habit or general appearancs 

 from each other, that several genera might be instituted from the single Linnaean genus. This how- 

 ever is not necessary, though it has been done by Muller and others. It should however be observed 

 that the title Monoculus, applied to this genus by Linnaeus, was given on account of the close ap- 

 proximation of the eyes, which in some species appear single. It must therefore be confessed that 

 Linnicus has somewhat unhappily distinguished the whole genus by a name which can only be ap- 

 plied with strict propriety to some particular species. Of those described in the present paper by 

 Mr. Muller, the most common is the Monoculus conchaceus of Linnaeus, a very frequent inhabitant 

 of stagnant waters, and which has so much the appearance of an extremely minute muscle, that 

 it has often been mistaken for such, by those who have attended to the shell alone, without consider- 

 ing the insect. 



Mr. MuUer's list of the Monoculi inhabiting the waters about Fridericksdal is here omitted, as, 

 being unaccompanied by figures, it could have been of no service; but it may be necessary to add, 

 that he has, since the publication of this paper, been the author of an admirable work, in which the 

 several species observed by himself are excellently described and figured. 



