60 BULLETIN OF THE 



The fact that two of the genera were precisely equivalent to those 

 of Professor Edward Suess ought to have secured some credit, at least 

 among his admirers, for the twenty-odd other precisely equivalent 

 genera established by Professor Agassiz and myself; but such has not 

 been the fact. 



Either we knew of Suess' publications and patterned after them, 

 only increasing the number of genera, or else the investigation was in- 

 dependent. Besides the fact, well-known to palaeontologists in this 

 country, that these investigations began some years before Suess had 

 published anything, there was no object in concealing our acquaintance 

 with his researches. On the contrary a prompt acknowledgment 

 would have been of great advantage, since it would have been easy to 

 show, that, in our much more complete classification, the genera were 

 founded upon the same system of characteristics as those used by 

 Suess to distinguish Lytoceras from Phylloceras. 



There has been nothing besides the above in the criticisms advanced 

 except general statements of disapproval, which, of course, cannot be 

 dealt with specifically and are of no imj)ortance. 



I will say, in conclusion, that I have nearly finished a very thorough 

 review of the same groups without being able to effect any very 

 material alterations. 



The same divisions are found to be sharply defined divergent series, 

 and whatever name or value may be given them, they are natural 

 groups ; this being so, my object is attained. 



This object is, as in the present publication, to obtain some faint in- 

 sight into the laws of descent of these forms one from another, by 

 means of such indications as may be afforded by a close study of the 

 developmental and adult characteristics, corrected or verified by the 

 observed geological positions of the species. 



Every one who has studied the coiled shells of Cephalopods and 

 Gasteropods, is aware that they retain in the interior of the umbilicus 

 the younger whorls, which are necessarily more or less covered up and 

 protected by those of later growth. By breaking away the older 

 whorls, one can therefore eventually arrive at those portions of the 

 involved cone which represent the very youngest periods of growth. 



This in Ammonites and Goniatites has been shown to be a minute 

 globular sac. In Nautilus, however, this sac is not retained, but traces 

 of its former existence are apparent on the apex of the first whorl, in 



