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island : but all these minute shells differ so essentially from the fossil 
shells of this genus, as to fully authorize the arranging of them under 
distinct genera. 
The number of species in the genus Ammonites must have been 
exceedingly great. Langius and D’Argenville, indeed, are very re- 
stricted in their enumerations ; the former giving fifteen, and the latter 
only fourteen, as the amount. Bromel ascertained the existence of 
forty species, and Scheuchzer extended the number to a hundred and 
forty-nine ; whilst the assiduous Rosinus was led, by his inquiries, to 
believe them to be not less than three hundred. 
To form a fair opinion on this point would require the examination of 
several collections, where these fossils had been collected with a par- 
ticular view to this investigation. I am, however, satisfied that Rosinus’s 
number is that on which we may with most safety depend ; for, inde- 
pendent of the vast differences observable as to size, the various mark- 
ings on the sides of these fossils are sufficient to characterize a great 
number of species. Thus we have smooth, knobbed, striated, and 
grooved. Those which are ornamented with knobs, vary according to 
the intermixture of these, or the order in which they are disposed. 
Those which are striated, as well as those which are grooved, derive a 
vast variety of embellishment from the striae or grooves being straight 
or undulating, or partly straight and partly waved, from being bifur- 
cated, trifurcated, &c. ; or partly simple, and partly furcated. The 
species resulting from each of these must, it is evident, be very nume- 
rous ; but from the several intermixtures of, or changes among, these dif- 
ferent markings, the number must necessarily become exceedingly great. 
But besides the numerous species which are thus formed, a prodigious 
number more may be reckoned from the different markings and forms 
of the backs of these shells, on which are also exhibited every embellish- 
ment, almost, of which such a surface is susceptible. When it is con- 
sidered that each of the modifications of form, of the sides of the shell, 
may be combined with every different form which is assumed by the 
back ; and that the number of species thus yielded will be the number 
