84 MOLLUSCA FROM THE GREAT OOLITE. 



Trochotoma discoidea, Roemer, sp. Plate X, figs. 10, 10«, 103, 10c. 



?Trochus discoibeus, Roemer. 1836. Nordd. Oolith., p. 150, t. 11, fig. 12. 



— — B' Orb. 1850. Prod. Paleont,, p. 354. 



— — Bronn. 1848. Index Paleeont., p. 1300. 



T. Testa discoidea, plano-convexd, hasi concavd, lato-umbilicatd; anfractibus (3) depressis, 

 subconvexis, transversim lineatis, basi acutis ; aperturd transverse depressd, ovatd. 

 (Roemer.) 



Shell discoidal, slightly convex, base concave, widely umbilicated ; whorls (3) depressed, 

 rather convex, transversely lineated, lines impressed by closely-arranged longitudinal and 

 very fine oblique striae ; lines upon the base acute ; aperture depressed and excavated. 



We have never been able to discover an open fissure upon this small species, but the 

 general figure agrees with this genus so well that we have not ventured to assign it to any 

 other. Four lines are visible upon the lower and seven upon the upper face of the last 

 volution, which is angular or step-like ; the first two turns are smooth and rounded : rare. 

 Height 3 lines, basal diameter 7^ lines. 



Locality. Minchinhampton ; Coral Rag, near Hildesheim {Roemer). 



Stomatia, Lam. 1801. 

 Stomax, Mont/ort. 1810. 



Shell suborbicular or oblong, generally ear-shaped and depressed ; in most species the 

 spire is prominent, but not produced, nor elongated ; sometimes, however, it is very small, 

 marginal, and inconspicuous. Aperture mostly longitudinal; in some species nearly 

 orbicular ; in others much elongated ; always very large ; its edges entire, united, at the 

 upper part, and scarcely modified or altered in form by any portion of the last volution. 

 Volutions from two to four. (G. B. Sowerby.) 



From the characters of the aperture and the presence of the carina, we have 

 ventured to assign the following shell to the genus Stoma tia (Lam), from most of the 

 recent species of which it differs in having a depressed spire, and the lines of growth and 

 spiral striae very regular, and sharply defined. Should other specimens afford further 

 generic distinctions, we would suggest the name Megastoma for it. 



