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fossils on the study of which they were about to enter. The first 
author who attempted a better arrangement of Ammonites than 
existed in his time was Von Bucu. That illustrious man saw 
in the ramifications of the lobe-line on the mould beneath the 
shell of the Ammonite a character which he found to be definite, 
and varied in different forms; and by grouping all the similar 
forms alike and separating the dissimilar ones therefrom, he 
divided the Ammonite group into many families. The same 
method was followed and enlarged by D’Orzreny and Quensrepr, 
and subsequently greatly improved by Professor Suxss, who 
had begun to study the Ammonite shell from a new stand- 
point, derived from the great experience he had gained in the 
examination of many better specimens than had fallen to the 
lot of previous observers. Svxss’s paper Ueber Ammoniten, 
soon engaged the thoughts of several young Naturalists of the 
Vienna school, and it became the starting-point of a new 
investigation. Dr. W. Waacen led the way in two interesting 
papers, communicated to the Palwontographica and Benecke’s 
Beitriige, and the result was that the new arrangement of 
Suzss’s genera and others proposed by Waacen assumed the 
form of a new classification. The characters upon which the 
genera were established were—Ist, the structure of the lobes 
and saddles, with the various arrangements of the lobe-line, 
occupied a front rank; 2nd, the shape of the aperture of the 
shell and the development of the mouth-border were shewn to 
possess characters of importance in constructing the diagnosis 
of genera; 3rdly, the length of the body-chamber affords 
another character from which important deductions are made, 
seeing that the size of the animal must have been proportioned 
to that of its dwelling-chamber, as we see so well exemplified 
in the case of the Nautilus pompilius ; and as sometimes the 
body-chamber in certain groups extends to a whorl and a half 
in length, in others to one whorl, in others to one half or 
two-thirds of a whorl, it follows that the shape and size and 
structure of the mollusc must likewise have varied in these 
different groups. The fourth feature is the amount of involution 
of the whorls, or in other words the extent to which the one 
