444 Dr . broussonet’s Account of 
it is tlioiight to be, I proceed in the like manner, in compar- 
ing tlie terms , of the meafures of the other parts; b.ut the 
utility of thete meafures' is very apparent in the diftinguifhing 
of the Species of Tome genera which are fo natural as that of 
Cyprians, Clupea , and many others, of which the.fpecies could 
not be otherwife eafily diftinguifhed. I (hall inftance a fpecies 
of Perea deferibed in the Comment aril Petrdpdirani under the 
name of Perea acerina , by Mr. gueldenstaedt, which 
could not have been diftinguifhed from the Perea cernua but 
by the proportional meafures ; fin ce the Cernua has the body 
about three times longer than the head, whereas the Acerina 
has it but twice as long, thouglmby the other characters £ney 
are almoft indiftinguifhable. 
To exprefs the pofition of the fins briefly, and with all pof- 
iible accuracy, which, however, I think-may be very welhun- 
derftood by the deferibed meafures, I take the diftance ; from 
the upper jaw to the bafis of the pedtoral fin, and then. fee. info 
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 firfi: being from the head to the pe&oral 
fin 
The feales of the Ophiditim , which have been figured by 
rondel e this, 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 obferve, that the utility of this method of measurement will appear 
not only in diftinguifliing fifties, but alfo animals of other clafles, and particu- 
larly fnakes, which cannot be well determined otherwife. Belides, I do not 
know any author on fubje&s of natural hiftory,. who has adopted that method. 
7 been 
