NIAGARAN CEPHALOPODS 
295 
Shell straight, gradually tapering, slightly elliptical in trans- 
verse section. Surface of the shell and character of the septa 
not preserved in the material at hand. 
Siphuncle smooth, conspicuously segmented, sub-central in 
position, and round in cross-section. Each joint or segment fits 
down a short distance into the swollen and defiected summit of 
the one next older; the proximal edge of the septum passed be- 
tween this expanded top and the contracted base of the joint 
above ; the groove for its reception is very narrow and it extends 
inward for a distance of about one-fifth the radius of the seg- 
ment’s base. Fragments of the septa still remaining in the 
grooves are very thin. The plane of contact between two seg- 
ments is more or less oblique to the longitudinal axis of the si- 
phuncle ; the amount of obliquity depends on the eccentricity of 
the siphuncle,— in the specimens at hand the large siphuncular 
fragments show the greatest obliquity. 
Endosiphuncle central, its diameter about one-sixth that of the 
smaller end of the segment ; in some of the specimens it is open 
and in others filled with foreign matter. Between the endosi- 
phunele and the inner surface of the segments radiate vertical 
lamellae which in cross-section resemble the septa of some cyatho- 
phylloid coral. , At the constrictions between the segments the 
lamellae seem to be replaced by short cylindrical rings arranged 
concentrically between the endosiphuncle and the base of the 
septal groove. 
Measurements: specimen (a) diameter, greatest, 33 mm., 
least, 26 mm. ; length, 31 mm. ; obliquity, 97°. 
Specimen (b) three successive segments; diameter, greatest, 
30.2, 29.9, 27.0 mm. ; least, 26.0, 25.2, 25.0 mm. ; length, 25 mm. 
each; obliquity 92°. 
Specimen (c), four successive segments; diameter, greatest, 
20.1, 20.1, 19.0, 18.5 mm. ; least, 17.3, 16.5, 16.0, 15.2 mm. ; length, 
16.0, 16.0, 15.5, 15.2 mm.; obliquity, 92°. 
One very fine specimen in the university museum lies in a slab of 
cherty dolomite; only a cast of the shell remains, while dolomitization 
has entirely effaced all traces of the septa. On being removed from the 
quarry the slab was broken in such a way as to show the siphuncle in 
its relation to the original shell or conch. Seventeen segments are 
present. The specimen is ninety millimeters in diameter at the larger 
end and fifty at the smaller, and is approximately 420 mm. long. 
The rate of tapering indicates that it was at least twice this length 
