ENDOCEEATIDiE. 
161 
17 to 20. Septa distant from 1| to 3| lines, according as they are 
measured at the narrower or broader end of the siphnncle. The 
latter is apparently marginal. The walls of the siphnncle (and 
septa ?) are nsnally composed of orbicular chalcedony, formerly 
known as Beekite 
The rate of tapering of the shell cannot be precisely computed, 
but it was no doubt very high. JSTo trace of the outer shell-sculpture 
has been seen in any of the specimens examined. 
Fig. 19. 
Piloceras invagmatum, Salter. — S, 8, remains of septa ; Si, siphimcle, a little re- 
stored in the lower part, with ridges marking the attachment of the septa. 
(One half natural size.) 
Remarlcs. In the example I have figured above the septa appear as 
delicate lines upon the weathered surface of the rock. This is one of 
the specimens out of Mr. Peach’s interesting and valuable collection, 
the whole of which was very kindly entrusted to me for examina- 
tion by Mr. H. H. Howell, F.G.S., Director of the Geological Survey 
of Scotland. 
In this fine series of specimens I have been able to demonstrate 
nearly all the structures in the siphnncle, as well as some of those 
of the chambered portion of the shell, which have been so ably 
discussed by Sir J. W. Dawson and Prof. Hyatt. 
^ This name is now, I believe, no longer in use among Mineralogists. 
M 
