KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 23. N:o |2. 31 
The Nautiloid stage. Some specimens having both stages still in connexion allow 
the determination of detached pieces from the same strata as belonging to this species. 
They are faintly curved as a ÖCyrtoceras, the dorsal side being concave and the ventral 
one convex, cylindrical, quite circular in section. The shell is finely, transversally striated 
and also longitudinally crossed by fine folds. The apex is rounded, blunt, and does not 
show anv distinct scar. The septa are of the common watch-glass shape and as seen in 
fig. 34 a placed at irregular distances from each other. They have a distinct neck around 
the siphuncele. The siphuncle is as usual near the ventral side, narrow, tubular and its ele- 
ments of varying length, according to the length of the interseptal space, as common in 
this genus. 
There is a remarkable specimen, figured in f. 26—27. The Ascoceras shell is formed 
in uninterrupted continuation with the Nautiloid shell, but both are without the least 
trace of any septum. It may be that there had been septa, but that these have been 
destroyed during the process of the fossilization. But it seems more probable, that it had 
been evacuated by the mollusc, before it had had time to withdraw entirely from the 
Nautiloid and secrete septa in the Ascoceras shell. The body chamber of the Nautiloid 
continues or is changed into the Ascoceras and the dividing septum was secreted after- 
wards. Thus this specimen represents a shell in its earliest »Aphragmite» stage. In the 
figures 23—24 we have an interesting specimen still more advanced. The Nautiloid is 
seen beneath, with its straight tubular siphuncle, partitioned off by the septum of the 
truncature and in the Ascoceras only the first sigmoid septum is ready formed. 
A section (see fig. 25) shows how both the Nautiloid and the Ascoceras cohere 
through a common shell. The dividing septum of the truncature is lined from within 
the Ascoceras with a nearly twice as thick calcareous organic secretion, which is continued 
up along the sides of the Ascoceras. This shell consequently consists of two strata. 
The Ascoceras-stage. Shell short, laterally much compressed, ventral side regularly 
curved, the dorsal one straight, with the neck, which makes a fourth of the entire length, 
bent towards it. The ornamentation is nearly the same as in Glossoceras gracile. It 
changes with its position on the shell, being finer lower down and on the ventral side, 
coarsér on the neck. "The microscopic fine, transverse and imbricated lines are crossed by 
narrow longitudinal folds. 
There are four sigmoid septa in all the eight specimens which have been sectioned, 
One specimen, fig. 22 & a, is very remarkable in having four regular, Nautiloid septa 
secreted above the sigmoid ones in the cavity formed by their curves. This is a re- 
version to the original Nautiloid stage which also has been found in a few instances with 
others. See pl. IV fig. 34 where there are three adventive Nautiloid septa. With the 
septa also the character of the siphuncle is changed. 
In the enlarged figure 220b an organic deposit is seen above the fourth sigmoid, 
thickest in the angle where the septum joins the shell and then stretching up along this 
it thinns out. This deposit occurs also in all the other Ascoceratide though perhaps in 
none so evident as here. 
The siphunele is very peculiar in this species. The narrow tube which leads from 
the Nautiloid siphunele into the Ascoceratidan, is so much oblique that it leans against 
