135 



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 Rosin us 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 parti- 

 cular 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 ta 

 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 



