376 GASTEROPODA OF THE INFERIOR OOLITE. 



Description. — There are two sizes; the dimensions given are those of the 

 larger (fig. 14) : 



Height . . . . .16 mm. 



Width . . . . .15 mm. 



Spiral angle ..... 68°. 



Shell conical, not umbilicated ; spire acute and about half the entire height. 

 Number of whorls seven, slightly concave, distinctly separated by the suture, and 

 provided with spinous carinse 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 costae 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 costse, which almost obliterate the fine spiral ornamentation 

 noticeable in the younger shells ; these costas 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-he&s. An extremely rugose variety, referred with some doubt 

 to this species, was found in the Variabilis-he&s of North Nibley. 



Var. plicata, Goldfuss. Plate XXXII, fig. 2. 



Turbo plicatus, Goldf., 'Petref. Germ.,' pi. 179, fig. 3. Cf. also d'Orbigny, ' Terr. 

 Jur.,' vol. ii, pi. cccxxix, figs. 2 and 3, and Quenstedt, ' Der. Jura.,' p. 314, pi. xliii, 

 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 



