474 
Figs. 4and5. The siphuncle is very large and propiodorsan in the 
ephebic and gerontic stage. 
Litoceras. 
This genus was described in Genera of Fossil Cephalopods, page 
259. 
The siphuncle is very large and is dorsad or below the centre in 
adults, but is ventrad in Zztoceras Whitteavsi in the neanic and ear- 
lier stages, and is very likely ventrad in the young at some stage in 
all species, as it is in those of Schroederoceras that have been 
studied. The young are slightly costated also and the adults 
smooth, as in other genera of similar groups. The umbilical per- 
foration is of good size, and in the nepionic stage the shell is cyr- 
toceran and similar to the shells of Schroederoceras of the same 
’ group, but with much broader whorls and deeper umbilici. These 
differences are maintained in the later stages of growth, the whorls 
being much larger, broader and have in the ephebic stage similar 
abdomens and convex, divergent sides without umbilical shoulders, 
resembling the neanic stages of species of Schroederoceras. 
The increase by growth in the lateral diameters of the whorl is 
rapid, as in the young of Schroederoceras and other allied genera, 
but it continues longer, and even the adults may have very broad 
whorls, so that these adults resemble in form the neanic stage of 
Schroederoceras. 
The aperture is less compressed than in the full-grown shells of 
Schroederoceras, and resemble those of the anephebic stage of that 
genus, but are not flaring or trumpet shaped, as in Trocholites. 
In fact, there has been a slight turning in of the edges in all the 
specimens observed, but this, however, may be due to compression. 
The hyponomic sinus is smaller and shallower than in the ephebic 
aperture of Schroederoceras. 
The contact furrow is broader and deeper than in Schroed- 
eroceras and the involution more marked on account of the rotund- 
ity and breadth of the abdomen, which is covered in. 
The end of the whorl, even in full-grown shells, is not free, and 
in this respect also the species resemble the neanic stage in 
Schroederoceras. ‘The living chambers are, so far as observed, 
longer than in Schroederoceras and shorter than in Trocholites. 
The sutures have deep dorsal lobes, saddles on the lines of 
