ENDOCEEATID^. 
159 
Durness specimens, however, it is not an uncommon thing to find 
two or three of the sheaths preserved, their walls standing out in 
relief from the surrounding matrix, which has been removed by 
weathering. 
Fig. 17. I. Section of siphuncleof Piloceras, sp., from Durness, showing two of 
the funnel-shaped sheaths, s : e, the endosiphon, with r, remains of former 
sheaths?; w, matrix filling what remains of the cavity of the siphimcle; 
q, quartz-infilling. II. Posterior extremity of another siphuncle much 
eroded, but showing an aperture, a, at the apex, by which the endosiphon 
may have communicated with the initial chamber ; iv, wall of the siphuncle, 
and q, quartz forming the infilling between this and one of the sheaths. 
III. Transverse section of another siphuncle, showing in the centre the 
endosiphon e, and what appears to be a partition p, representing perhaps 
the septum or “ central shelly plate” of Dawson. (All the figures are of 
natural size.) 
Fig. 18. Vertical section of an imperfect siphuncle, with a few of the septa 
attached, of Piloceras amplum, Dawson, cut in the direction of the shorter 
diameter of the shell, which was of an elliptical form, judging by that of 
the siphuncle ; sw, shell-wall ; sc, siphuncular cavity ; sh, sheath ; w, 
internal wall of siphuncle ; s, s, septa ; b, broken extremity of sifjhuncle ; 
r and e, same as in fig. 17, 1. The dotted lines are restorations. (Slightly 
reduced from Dawson’s figure, which is itself a little smaller than the 
original specimen.) 
A series of short, upwardly projecting lines are observed to spring 
from the sides of the endosiphon (figs. 17 and 18), where it is slightly 
swollen. These lines are conjectured by Dawson to be the remains 
