127 
TROCHUS concavus. 
TAR. CCLXXII.— Fig. 1. 
Spec. Char. Conical, smooth ; base carinated ; 
volutions concave above, convex below ; mar- 
gin and base striated. 
Somewhat related to the British Trochus Ziziphinus, 
but taller, smoother, and having the upper half of each 
whorl concave, the other half being concealed ; the 
edge is obtuse, faintly marked with elevated striae ; the 
striae upon the base are strongest towards its centre ; 
aperture rhomboidal ; umbilicus closed. 
Found in the Crag of Suffolk, by Professor Sedgwick; 
the shell is very tender, and still retains much of its 
original pearly lustre beneath its opaque coat. 
TROCHUS imbricates. 
TAB. CCLXXII. — Figs. 3 and 4. 
Spec. Char. Pyramidal, with several transverse 
threads upon each whorl, crossed by fine lon- 
gitudinal striae, whorls angular, imbricating, 
flat above, very convex beneath. 
Almost half as tall again as wide : the angular shape of 
the volutions gives the spire the form of a screw ; the 
base is very convex, and striated in the same manner as 
the rest of the shell ; umbilicus closed. 
Found in clay near Cheltenham by Miss E. Warne, 
to whom I am indebted for the only specimen I have 
seen. 
