PROSOBRANCHIATA. 235 
of granulations are more numerous, and the margins of the whorls present, in addition 
to the sutural row of beads, three very slender concentric lines granulated by the lines 
of growth of the sinus. It has been before stated that one of the more prominent 
characters of the true P. ¢erebralis is taken from the perfectly smooth concave margins 
of the whorls; and the granulated margins in the present case would apparently 
indicate a distinct species; but the occasional occurrence of a plicated margin in the 
last variety prepares the way for the present form; and as this agrees in all the more 
important characters with the variety ditropis, I have regarded it as merely another 
variety of P. terebralis. 
The shell in the variety gyrata (fig. 10 6—d) is smaller than that of the type, and 
doubly keeled; but both keels are thick, band-like, and strongly and obliquely plicated, 
and have a denticulated appearance from the plications being continued over the edges 
of the bands; the plications, following the curve of the line of growth, are less oblique 
on the anterior keel than those on the posterior keel. A single slender raised line, 
finely granulated, traverses the space between the keels; the front part of the whorl is 
ornamented with several concentric raised lines, granulated with great regularity ; of 
these, the one next to the anterior keel, in some specimens (as in fig. 10 4), and that 
next but one, in others (as in figs. 10c and ¢), is the thickest and most prominent ; 
the others slightly diminish in size as they approach the anterior extremity of the 
canal. 
The next variety, pulcherrima (fig. 10 e and g),* appears to correspond with the 
variety a from Compicgne, noticed by M. Deshayes. In this variety the shell is small 
and doubly-keeled; the posterior or shoulder-keel denticulated, the anterior keel 
rounded and obscurely plicated, almost smooth; the front part of the whorls is 
ornamented with several distant, thickish, concentric lines, which also are smooth and 
simple, or but very feebly granulated; the whorls are bordered round the suture by a 
thickish raised line, obscurely granulated or plicated; the margins and the spaces 
between the keels and between the concentric lines are perfectly smooth. 
The variety revoluta (fig. 10 f) is a modification of the variety pu/cherrima ; in it the 
sutural edges of the whorls are very faintly crenulated; the shoulder-keel is sharp, 
obscurely plicated and denticulated, and the edge is bent upwards: the anterior keel is 
round and feebly plicated, and the concentric lines are slender and finely granulated. 
In the last variety to be noticed, the variety Pagoda (fig. 10 4), the granula- 
tion and denticulation, which in the typical form and the preceding varieties form 
more or less prominent characters, are wanting; and a new mode of ornamentation 
prevails. In this variety the shell, which is relatively wider, is doubly-keeled, and 
ornamented with simple spiral bands; the margins of the whorls are concave, and 
* TI have adopted for the shells forming this variety, the name by which they have been distinguished 
as a species in Mr. Wetherell’s cabinet. 
