444 Dr. broussonet’s Account of 
it is thought to be. I proceed in the like manner, in compar- 
ing the terms of the mea lures of the other parts; but the 
utility of thefe meafures is very apparent in the diftingu idling 
of the fpecies of lome genera which are fo natural as that of 
Cyprinus , Clupea , and many others, of which the fpecies could 
not be otherwife ealily diftinguilhed. I lhall inftance a fpecies 
of Perea deferibed in the Comment arii Petropolnani under the 
name of Perea acerlna , by Mr. gueldenstaedt, which 
'Could not have been diftinguidied from the Perea cernua but 
by the proportional meafures ; ftnee the Cernua has the body 
about three times longer than the head, whereas the Acerlna 
has it but twice as long, N though by the other characters they 
are almoft indiftinguilhable. 
To exprefs the pofttion of the fins briefly, and with all pof- 
fable accuracy, which, however, I think may be very well un- 
derflood by the deferibed meafures, I take the diftance from 
the upper jaw to the bafts of the peCloral fin, and then fee into 
how many equal parts the whole body may be divided, and to 
thefe parts I apply the name of regions; I meafure them to 
the extremity of the middle of the fin of the tail, and I 
exprefs the pofition of the fins as follow : D. 3. 4. A. 3. V. 2. 
P- 2* the letters being the initials of the fins, and the numbers 
of the regions, the firft being from the head to the pe&oral 
fin 
The feales of the Ophidium , which have been figured by 
itoNDELETius, but overlooked by many other writers, have 
* I beg pardon for the digreffion ; but I thought it would not be improper in 
this place to obfer\*e, that the utility of this method of meafurement will appear 
uot only in diftinguiflving fifties, but alfo animals of other claflfes, and particu- 
larly fnakes, which cannot be well determined otherwife. Befides, I do not 
■know any author on fubje&s of natural hiftory, who has adopted that method. 
j been 
