[ 24-1 ] 
Syflematical writers have confounded aquatic infedis, 
very different, both in fpecies and genus, under the 
general arbitrary name of MonGculus, They have 
not been contented with giving the lame denomi- 
nation to feveral fpecics, whole properties and attri- 
butes did not at all correfpond with the known dia- 
raders of the genus, but have likewife given as Ipc- 
cilic marks thole which nature tells us are generic. I 
liiall only mention at prefent the jlrdid, which farnilhes 
me with a fl:riking example. M., Geoffroy, as well 
as Linnaeus, has ranked it under the genus of the 
monoculi. According to the latter, the generic 
charader of this, is to have two eves and twelve- 
feet, hx of which are fixed • whereas the former 
gives it only one eye and fix feet. Befides the differ- 
eiice as to the number of eyes, my defeription proves 
that the number of feet does not agree with this 
account. Let me add, that the particular make of 
the antenna;^ the feet, the tail, and the whole body,, 
give this infeff a claim to form a genus of its own. 
As to the fpecific definition, Antennis 7nuhipliclhtis 
capillaceis^ tejia bivahi, and vehatever elfe is laid of 
it, if one excepts the colour only, belong equally to. 
all my fpecies with capillary antemue, and conftitu-te 
rather a defi.itition of the whole genus, tlian of a. 
particular fpecies. 
The fame miflake is to he met with in feveral other 
fpecies brought under this genus ; and the realbn- 
of it is that the authors, not havinc^ known more than 
four of all the different fpecies, which I have reckoned 
up in the following table, have generalized the cha- 
raders of thefe four, though they were not, well 
acquainted even with thefe. 
Vol.-LXL I i The. 
