The Genus JSFanno, Clarke. — Hyatt. 7 
Thus it seems clear that in JSTaimo, and possibly in Sannioni- 
tes, in which genus the endosiphon is often absent in adults, 
this organ is clearly a characteristic of the metanepionic sub- 
stage. 
The opening through the apex of the empty, siphonless 
shell in the anepionic substage was not an endosiphon but a 
primitive organ or protendosiphon probably communicating 
with the protoconch. 
The true endosiphon was formed by the tip of the swollen 
sheath while it was building the first endocone, which there- 
fore belongs to the middle nepionic substage. Upon the en- 
try of the animal into the paranepionic substage a rupture of 
the sheath and endosiphon took place and the sheath in clos- 
ing at the apical end plugged up the endosiphon and began 
to build the loose filling immediately apicad of the tip of the 
second endocone. The second endocone was built as shown 
by Clarke's figure 8 and this figure 2, as the siphon was be- 
coming contracted and it was completed after the siphon had 
assumed the proportions of the ephebic siphon so that this 
endocone should be reckoned as belonging to the ananeanic 
substage. These materials give the approximate!}^ exact his- 
tory of these substages but they plainly show that the nepi- 
onic stage had an endosiphon which was lost at the termina- 
tion of this stage and that at the beginning of the neanic 
stage there was still a large sheath with a more or less conical 
end, as in figure 2 and Clarke's figure 8, quite dirt'erent from 
the elongated tubular termination of the same organ in the 
ephebic stage as shown in figures 1 and 3, yet agreeing with 
it sufficiently in figure 1 and Clarke's figure 8, to make it highly 
probable that the older sheath is only a shrunken modifica- 
tion of the ananeanic sheath. 
This result does not in the least contradict Prof. Clarke's 
result that Xanvo did not have an endosiphon, on the con- 
trary it confirms this point and adds simply the fact, that this 
genus possessed an endosiphon only in the young and was 
probably therefore, a modified descendant of Endoceras wh'xch 
had this organ throughout life. 
The original of Clarke's figure 3, having been cut by him, 
shows some extremel}^ interesting and novel characteristics. 
The sheath is shown in plate I, figure 3, terminating abrupt- 
