GASTEROPODA. 83 



TROCHOTOMA TABULATA. Plate X, figs. 17, 17 a. 



T. Testa conicd, apice acuto, anfractibus (5) tenuissime striatis subquadratis, media 

 angulatis ; anfractu, ultimo subangulato ; basi planato, profunde excavatd. 



Shell conical, apex acute ; whorls 5, very finely striated, step-like, and angulated in 

 their middle portion ; the last whorl is angulated, the base flattened and deeply excavated. 



The sides of the volutions are nearly flat, both above and beneath the angle, which, 

 together with the srnallness of the encircling rib, fineness of the striae, and acute apex, 

 serves to distinguish it from T. calix or T. affinis, Desl., which is an Inferior Oolite species. 

 It is moderately common. Height 10 lines, basal diameter 12 lines. 



Our figure is of medium dimensions. 



Locality. Great Oolite of Minchinhampton. 



TROCHOTOMA OBTTJSA. Plate X, fig. 15, b. 



T. Testa turbinatd; apice obtuso; anfractibus (5) convexiusculis, striatis, basi dilatatd, 

 media late excavatd; peripli&rid striata. 



Shell turbinated ; apex obtuse ; whorls (5) rather convex, striated, the lower surface 

 dilated, its middle widely excavated, periphery striated. 



The encircling rib is large but depressed, and contributes to give a convex aspect to 

 the whorls ; the striae are large, the general figure being more turbinated, or less regularly 

 conical than is usual with the Trochotomce, each advance of growth was equal to two thirds 

 of a volution : it is by far the most abundant of the genus. Height 10 lines, basal 

 diameter 13 lines. 



Locality. Great Oolite of Minchinhampton. 



TROCHOTOMA EXTENSA. Plate X, figs. 19a, 195. 



T. Testa conicd; apice obtuso, depressd; anfractibus (4, 5) subangulatis, planis, et 

 leevibus; basi ampld, profunde excavatd. 



Shell conical; apex obtuse, depressed; whorls (4, 5) subangular, flattened, and 

 smooth ; base wide, rather convex ; cavity large and deep. 



This is by far the largest and most rare of the Great Oolite species, the base is 

 enormously wide, and the cavity very large. Height 16 lines, basal diameter 30 lines. 



Locality. Minchinhampton. 



