CHEPHALOPODA. 771 
Nanno aulema.] 
interrupted. One of the specimens has the wall of the conch adhering to the 
siphonal wall along this surface. The same fact is shown in Holm’s figure of 
Endoceras (Nanno) belemnitiforme. It will be observed from the figure that the 
cylindrical portion of the sipho has about one-fifth of the diameter of the entire 
shell at its widest point. 
Upon examination of the interior structure of these siphones they are found to 
be completely solid in the apical portion for usually about one-half the length of the 
preeseptal cone, but in some instances this solidification extends for the entire length 
of the cone and into the cylindrical part of the tube. The cavity of the sipho above 
this filling is a narrowly conical chamber whose walls gradually become thinner 
from the apex upward, their upper edge appearing to be rounded off and finished. 
The substance of the siphonal cone and walls is invariably very compact, 
radially crystalline calcite, indicating, inasmuch as all the specimens have been 
found in calcareous shales and clayey limestones, a simple modification of the original 
organic deposit; the internal cavity is filled with the mud of the sediment. Cross- 
sections of the cone in both directions show evidence of a dark, concentric, presum- 
ably organic discoloration, which may represent an internal sheath, but this seems 
the less probable as this layer affords no surface of easy displacement of the parts, 
nor does the radial structure of the calcite appear to be at all interrupted by it. I 
should be disposed, rather, to regard it as a trace of an organic remnant of the 
fleshy sipho, left in its anterior progress with the growth of the shell. 
The sections have afforded no evidence of a tube connecting the apices of these 
sheaths, the endosiphon of Hyatt. The addition of the septate portion of the shell, 
as shown in a single specimen which appears to be nearly complete, gives the species 
a fusiform and symmetrical appearance, broadest below the aperture, the sipho 
seeming to extend nearly the entire length of the shell. The septa are 
gently and regularly concave, slightly inclined toward the sipho, and there were 
apparently about twelve in the length of the shell as preserved. The first septum 
seems not to conform to the contracted surface of the cone which has a much greater 
obliquity, and thus the first air-chamber appears to be an irregular, wedged-shaped 
cavity between these two surfaces, but there is no evidence whatsoever that the 
conical end of the sipho was in any way involved in this cavity except at its proxi- 
mal surface. The apical cone was unquestionably external except so far as 
ensheathed by a mere coating or film of the shell-tube. 
The dimensions of these specimens are as follows: A nearly complete sipho 
has a length of 36 mm.; its greatest width is at 19 mm. from the apex and measures 
10 mm, in major, and 8.5 mm. in minor axis; its apertural diameters are 8 and 6 mm. 
