226 
SERPULA tricarinata. 
TAB. DCVIIL—figs. 3. & 4. 
Seec. Cuar. Repent, rather smooth, but some- 
times when old squamose, round, with three 
thick keels, the central one largest ; keels en- 
tire, sometimes disappearing. Aperture round 
with two thick lobes at the base, the edge thin. 
Sexpom so thick as a goose quill, tapering rather 
quickly, the surface of attachment is expanded until the 
shell is old, when the last portions are nearly cylindrical 
and often free from keels, its surface is then squamose. 
Among the squame in such individuals, or between the 
lines of growth in others, there are frequently minute 
pores or short tubes, but whether formed by the animal of 
the Serpula or some minute one is not easily discovered. 
The specimens figured are from the Calcareous Grit of 
Shotover Hill.. We have others, that appear precisely the 
same, from the Coral Rag at Steeple Ashton, and from 
the Cornbrash of Felmersham, the latter collected by the 
Rev. T. O. Marsh: it is also found in the Diluvium of 
Norfolk. We have sometimes suspected it to be the Ser- 
pula intestinalis of Phillips’s Geology of Yorkshire, but 
in the absence of description we cannot tell whether that 
be a decurrent species or not. 
