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. terebralis 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 b — 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£), and that 

 next but one, in others (as in figs. 10c and d), is the thickest and most prominent; 

 the others slightly diminish in size as they approach the anterior extremity of the 

 canal. 



The next variety, palcherrima (fig. 1 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 revolula (fig. 10/) is a modification of the variety pulcherrima ; 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 h), 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 



* I have adopted for the shells forming this variety, the name by which they have been distinguished 

 as a species in Mr. Wetherell's cabinet. 



