The Genus Nanno, Clarke. — Hyatt. 5 
The matrical filling of the endosiphon tails out internally, 
disappearing in the organic, calcareous, white deposits. The 
form of the filling proves clearly that the ananepionic endo- 
siphon was open to the exterior like the sheath above and 
that it was closed during the life of the animal by internal 
deposits which did not completelj^ fill the tube but left an ir- 
regular conical hollow at the tip which was plugged up by 
the ferruginous matrix after the death of the animal. The 
exact time of the internal organic closure was probabl}' at the 
end of the paranepionie substage or beginning of the next or 
neanic stage. This young endosiphon in other words pene- 
trated the first endocone and belonged to the same substage. 
The earlier substage when the siphon was empty must have 
possessed a simple aperture connecting with the protoconch. 
To make this clearer to readers unfamiliar with recent inves- 
tigations among cephalopods it is necessary to interpolate a 
short description of the stages of development among these 
forms. 
The protoconch or earliest embryonic stage of the shell is 
supposed to have preceded the formation of the tip of the 
conch and to have communicated with the first living cham- 
ber in this tip through the endosiphon. This is naturally 
called the '"prosiphon" by Zittell on account of its position, 
but the author considers it as not proven that this organ is in 
any sense a siphon. On the other hand it is when complete a 
differentiation of the tube formed by the tip of the sheath 
and it is at all stages distinct from the funnels of the sur- 
rounding siphon. The siphon is built up by the funnels 
which are formed by a ditt'erentiated zone at the base of the 
mantle, whereas the endosiphon is built by the probably thin- 
ner walls of a prolongation of the mantle called the fleshy 
sheath. There is always a sharp distinction between the in- 
ternal deposits of the fleshy sheath and the funnels both in 
position and structure. 
The ananepionic substage is a septaless living chamber with 
a cicatrix, oval or round in Endoceratidai, the metanepionic 
has septa and a huge empty siphon, which in Xanyw practi- 
cally fill the interior of the apex, the paranepionie sub- 
stage has a similar siphon but with the first endocone and an 
endosiphon formed in the apex and continuous witii the open- 
