274 Mr. Laruam’s Effay on | 
that were only a fingle fpecies known to me, as was fuppofed by 
the ancients, 1 fhould moft certainly join in the received opinion of 
placing it with the Sharks, though differing in fome particulars, 
rather than to form a new genus for it. 
It has been urged, that the difference of fhape and fize of 
the fpines in the fnouts of various fubjeéts may arife from age or 
' fex: the latter I cannot deny, as far as relates to the two firft de- 
{cribed, as the fpines refemble each other more than thofe which 
follow; yet in regard to the firft two, whoever will make a fair 
comparifon will moft probably join with me in feparating them, 
till we have fufficient authority to unite them into one fpecies. 
The number of fpines alfo, were no other diftinétion manifeft, 
will of itfelf be fufficient to form a precite character for dividing 
the feveral fpecies. 
Klein obferves, that in the embryo ftate the fides of the fnout 
are as {mooth as the gums of a new-born infant; but, in this cafe, 
we are inclined to think that the fpines make their appearance not 
long after its exclufion, and that they grow very quickly; for in a 
fpecimen of the fecond fpecies, now before me, the total length of 
which I conjecture to have been about thirty inches, the {pines 
are full one-fourth as long as thofe of a nearly full grown fpeci- 
men in the Leverian Mufeum. Another obfervation may likewife 
be drawn from the comparifon of the fnouts of the fmaller fized 
with the full grown ones; for as fome have been met with which 
meafured only eight inches, and contained from thirty to thirty- 
four {pines on each fide; and others, of the very fame fpecies, of 
three feet in length, in which were found no greater number; may 
we not fafely conclude, that they do not increafe by being fhed 
_in the firft ftages of life, to be replaced by others, as in the jaws 
of the human fpecies, and thofe of quadrupeds ? 
The 
