494 UNITED STATES GEOLOGICAL SURVEY OF TOE TERRITORIES. 



other sections do. Indeed, this character is so strongly marked in this type 

 that I would scarcely hesitate to admit the section as a distinct genus, if it 

 were not that we find among extinct species many intermediate gradations 

 in this character of the septa. 



I am now much inclined to believe that the shell for which Montfort 

 proposed the name Aganides in 1805 is identical with Hercoglossa, Conrad, 

 1866. At one time, I was strongly inclined to adopt the conclusion main- 

 tained by some, that the type of Montfort's genus Aganides is a Goniatite, 

 which latter name would, in that case, be only a synonym. In the only copy 

 of Montfort that I had then seen, his figure of the type of his proposed genus 

 Aganides does not show the position of its siphuncle clearly, though there is 

 some appearance of an attempt to represent it in a central position (he does 

 not mention in his description the position of the siphuncle). In another 

 copy, however, belonging to the Congressional Library, the siphuncle is 

 plainly seen, in the same figure, in a central position. I have also since 

 ascertained that the original figure in Sonini's edition of Buffon, from which 

 Montfort's illustration of the type of his Aganides was copied, shows clearly 

 a very nearly central siphuncle. Consequently, if correctly drawn, the fossil 

 represented cannot be a Goniatite, but might be a Hercoglossa, or possihly an 

 Aturia. The locality (Namur) cited both by Sonini and Montfort, however, 

 would be much against the conclusion that it belongs to either of the latter 

 two genera, and favors the opinion maintained by d'Orbighy and some others 

 that it is a Goniatite, the rocks at Namur being, if I am correctly informed, 

 of Carboniferous age. Until the question in regard to Montfort's type can 

 therefore be definitely settled, it would be improper to make his name 

 replace any one of those mentioned. 



The genus Nautilus, as here understood, dates far back into the Silurian 

 epoch, ranges through all succeeding formations, and is still represented by 

 a few living species in our existing seas. Since the origin of the group, how- 

 ever, during the Silurian period, it has developed at different times mark- 

 edly different characters, sending off as it were branches and subbranches in 

 various directions, until, in some cases, these sections have diverged so far 

 from the original central idea, so to speak, of the genus, as to give origin to 

 serious doubts whether the whole should be included in one genus. Although 

 these different characters were from time to time developed, the typical sec- 

 tion of the genus never entirely died out ; and it is somewhat remarkable 



