94 BULLETIN OF THE 



young. The siphonal coecum is entirely made up of the funnel of the 

 first septum. The funnels of the second and third septa are excessively 

 long, but in the fourth a decided decrease in this respect is noticeable, 

 and on the fifth septum it assumes very nearly the short aspect of the 

 same part in the full-grown shell. The lips of the funnel incline inward, 

 resting upon, and surrounded by, the looser-textured wall of the siphon, 

 which reaches exteriorly considerably beyond the lips of the funnel in 

 the young, and in the adult sometimes to the bottom of the septum it- 

 self. Barrande describes the length of the funnel as exceedingly vari- 

 able in the Silurian Nautili; but this does not appear to be true among 

 the modern forms. I was unable to determine whether the funnel in the 

 Jurassic Nautili was longer in the young than in the adult. It is proba- 

 ble, however, that, as in other characteristics, this will be found to have 

 acquired greater constancy, as we proceed in time ; in fact, the funnels 

 of the young Nautilus Pompilius, invariably longer than those of the 

 adult, show that the length has not only become more constant, but has 

 even been reduced, in accordance with the law of acceleration, to an 

 embryonic characteristic. 



Sandberger and Barrande, who have studied the siphonal funnel more 

 than other authors, use a somewhat different terminology, the former 

 speaking of it as a funnel and the latter as a conical neck. I prefer 

 Sandberger's term, because it seems to me to express the form quite as 

 well as the latter. In all the species that I have examined, whether 

 Nautili, Goniatites, or Ammonites, the aperture is always somewhat 

 wider than the bottom, and one side, the ventral, inclined, the opposite 

 being more abrupt. 



In other Nautili, however, the funnel form is more distinctly expressed, 

 as in Nautilus zic-zac. Here the structure which I have described, tin; 

 continuity of the outer layer of the siphon or sheath with the septum, 

 is most, plainly expressed. The siphonal funnels in the adult extend 

 posteriorly, as in the young Nautilus, to the opening of the next younger 

 funnel. They become narrower posteriorly, until near the junction, and 

 then a tumid band plugs up completely the siphon, some distance outside 

 of, or posterior to, the flaring sides of the funnel. In other words, the 

 funnels set into, and not upon, each other, like a pile of the necks of 

 broken bottles, when the septa are fractured in order to expose them to 

 view. The shell of the funnel throughout is of the same clo-e, pearly 

 texture, except the swollen band at the junction. "When this is more 



