376 GASTEROPODA OF THE INFERIOR OOLITE. 
Description.—There are two sizes; the dimensions given are those of the 
larger (fig. 14): 
Height “ : - : . 16mm. 
Width , : : : = 1S mm. 
Spiral angle . : = 687 
Shell conical, not umbilicated ; spire Soute and phone half the entire height. 
Number of whorls seven, slightly concave, distinctly separated by the suture, and 
provided with spinous carine on the posterior and anterior margins; there is no 
spiral ornamentation in the interspace, but in the younger and better preserved 
specimens a system of radial costes connecting the spinous points may be noted. 
A fine system of growth-lines is associated with this ornamentation. 
The body-whorl is large and sub-bicarinate ; in the older shells the posterior 
row of spinous tubercles becomes indistinct towards the aperture, whilst the 
double carina is markedly spinous. The base is very full and puckered by a 
rugose system of axial coste, which almost obliterate the fine spiral ornamentation 
noticeable in the younger shells; these coste terminate in an irregular semicircle 
of large tubercles around a slight umbilical depression. Aperture subrhomboidal, 
the height and width being nearly equal, with a considerable callus on the rounded 
inner lip. 
Relations and Distribution.—The chief point of resemblance in this species and 
T. duplicatus consists in a tendency to a duplex keel towards the basal periphery. 
T. subduplicatus is rugose, though wear and other causes may somewhat modify 
this peculiarity. There is also some variation in the size of the umbilical 
depression, though no true umbilicus exists; there is likewise considerable 
variation in other respects. 
T. subduplicatus is probably better known as a fossil of the Upper Lias. 
Characteristic specimens, such as those figured, occur at Newton (Yeovil Sands) 
in the Dumortieria-beds. An extremely rugose variety, referred with some doubt 
to this species, was found in the Variabilis-beds of North Nibley. 
Var. puicata, Goldfuss. Plate XXXII, fig. 2. 
Turbo plicatus, Goldf., ‘Petref. Germ.,’ pl. 179, fig. 3. Cf. also d’Orbigny, ‘ Terr. 
Jur.,’ vol. ii, pl. ecexxix, figs. 2 and 3, and Quenstedt, ‘ Der. Jura.,’ p. 314, pl. xl, 
fig. 19. Both d’Orbigny and Quenstedt agree that this form is only a variety of 
the preceding; the latter author observed that it is a somewhat simpler 
modification. 
This modification consists chiefly in the fusion of the duplex carina of the 
