10 
TRIGONIA Pullus. 
TAB. mill.— jigs. 2 and 3. 
Spec. Char. Obovato-triangular, with transverse 
smooth ribs ; posterior side obliquely trun- 
cated, marked with several crenulated ridges 
and bounded by a strong crenulated keel ; lu- 
nette large,, regularly striated across. 
This so nearly resembles T.costata(M.C.tab.85.), that 
it is doubtful whether it may not be the young state : the 
only marked difference, except size, is the regular some- 
what curved set of elevated lines that cross the lunette 
at right angles with the edge of the shell, in place of 
irregular lines of growth ; the form is not quite so an- 
gular, and the ridge that separates the posterior side pro- 
jects beyond the edge. 
I am not acquainted with the locality of the specimen 
fig. 2, but it is evidently from the same kind of stone as 
the smaller ones, fig. 3, which are from Ancliffe. 
There is in the Green-sandstone at Hythe in Kent, a 
Trigonia much resembling T. costata ; but the speci- 
mens that have come into our hands are too imperfect 
to describe, or even to distinguish : it appears to have 
fewer ribs. 
