KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 23. N:o |2. 37 
uppermost is the most narrow and the edges of the fifth and fourth are seen beneath the 
edges of the sixth. The bottom of the lacuna is formed by the third septum (4A. fig. 15). 
The exact boundary line of the sixth septum around the siphuncle is copied in fig. 14. 
The siphuncele (fig. 10, 10a) consists of five nummuloid elements, of which the 
uppermost, owing to the extreme obliquity of the septa near the convex side, are irregu- 
lar. The ratio of the diameters in the lowest elements is as 3 : 5 or the same as in 
the former specimens. The necks of the septa are very large and when seen from below 
(f. Sa, 8) they resemble a button. When the truncation has taken place, the aperture 
of the siphuncle has been closed by a peculiar secretion, resembling a little plug (pl. VI 
f. 8, 8a, 10 a). I suppose that this has been effected from within, as there is no trace 
that the truncated part has been strengthened from without and there only is the thin, 
lowest septum occupying the place of an outer shell. Some specimens, as that delineated 
on pl. VII f. 1, 2, have seven septa, viz. three complete and four lacunose. 
On the nucleus of the shell (fig. 14) there are (b) several impressions of the in- 
terior surface, showing longitudinal lines and a serrated edge. On the superior surface 
of the septa there is along the upper edge a row of small pits (74 c) and also on the 
inferior surface (fig. 13 x). 
The way in which the decollation was effected may be seen in a section given pl. 
VIT fig. 17. The shell has burst just below a septum and thus laid it bare. 
