GASTEROPODA. 33 



N. Testa turrito-conicd, spird angido 18° — 22°, anfractibus subplanis inornatis; colu- 

 mella crassd, prius solidd denique perforata, plicas duas parvas, remotas gerente; labro 

 dextro intus uniplicato, aperturd rhomboidali. 



Shell elongated, conical, smooth ; in its young state there is usually a slight depression 

 round the lower part of each whorl, this is gradually lost in the larger whorls, which are 

 quite flat; but specimens may be found in which all the whorls are slightly convex. The 

 columella is solid in the young shell ; but usually becomes perforated about an inch below 

 the apex ; there is great variety in this respect in different specimens, the perforation some- 

 times commencing within half an inch from the apex, while other shells, an inch and a half 

 long, may be found quite solid. The spiral angle also varies from 20° to 22° in different 

 specimens ; in some instances the sides of the shell are straight, in others the lower part is 

 more cylindrical than the upper ; in some few instances the lower part of the shell enlarges 

 more rapidly than the upper, in which case the perforation of the columella is unusually 

 large. Thus the species varies in its external form, from a neat, regular shell to a 

 very clumsy one. The aperture is rhomboidal, its height being half as much again as its 

 width, ending below in a short canal. There are three internal folds, viz.: one on the outer 

 lip, near to the base of the whorl, which is insignificant at the aperture, but long and strong 

 in the inner whorls; another, thick and blunt on the columella, a little below the preceding; 

 thirdly, one small and blunt on the top of the whorl. These folds are very constant in 

 form, and serve to distinguish the species readily. 



Sutural angle 90° to 95° 



Basal angle 125° to 130° 



Length, 1 inch to 2^ inches. 



In the young state, or when the axis does not exceed 10 or 12 lines, the aspect is so 

 dissimilar of this protean shell, that a particular description of that condition is necessary : — 

 It is taper and pointed, the volutions are convex, very narrow, an individual of 9 lines 

 having as many whorls. The sutures are very deeply depressed, the shell is altogether 

 delicate and fragile, but perfectly regular. Specimens exceeding 10 lines increase dispro- 

 portionally in the height of their whorls ; they become more flattened, the sutures are less 

 strongly defined, the shell acquires a considerable increase of thickness, and the whole is 

 changed. 



Locality. This specimen occurs in every stage of growth and throughout the entire 

 thickness of the formation in Gloucestershire; its habits were gregareous — the shelly 

 weatherstones more especially contain it in great numbers. 



NerinyEa (Trochalia) Eudesii. Plate VII, fig. 6, 6a. 



? Cerithium Defrancii, Deslongchamps. Mem. Soc. Linn. Normandie, vol. vii, pi. 8, 



fig. 36. 



N. Testa turritd, conicd, anfractibus (1 0) concavis, angustatis, lineis transversis cinctis 



