346 GASTEROPODA OF THE INFERIOR OOLITE. 
Crossostoma discoidewm and C. heliciforme, which he finally regarded as adult and 
discoidal forms of smooth ‘* Monodontas,” leaving only Crossostoma Prattii as the 
representative of the genus. This fossil was said to have come from the Inferior 
Oolite near Bath. I have not succeeded in obtaining a sight of the type. The 
genus is held to include Crossostoma (Delphinula) reflerilabrum, d’Orb., from the 
Lias. 
280. Crossostoma, sp.; cf. Crossostoma Prattii, Morris and Lycett, 1851. Plate 
RAVI Ges. 17 a2 17 5. 
1851. Crossostoma Prarrri, Morris and Lycett. Great Ool. Moll., pt. 1, p. 72, 
pl. xi, figs. 21, 21a. 
Cf. also Roretna Macrostoma, Stoliczka. Hierlatzschicten, p. 178, pl. iii, fig. 5. 
Trrnostoma Nrumayrt, Gemmellaro. Faune Giuresi, &c., p. 344, pl. xxvii, 
figs. 15, 16. 
Description.—Shell thick, nearly twice as wide as high, discoidal ; spire greatly 
depressed. The width of the figured specimen is 15 mm., and of a smaller one, 
which I possess, 10 mm. The body-whorl is essentially rotelliform, the aperture 
small and circular, and there is a considerable thickening towards the columellar 
extremity. 
N.B.—There is no umbilicus, as might possibly be inferred from the figure. 
Relations and Distribution.—The probable relations of this very discoidal shell 
are indicated in the list of references. It may be Crossostoma Prattii, but if so the 
figure in the ‘Great Oolite Mollusca’ is not sufficiently discoidal. The form is 
very rare. The figured specimen is a brown ferruginated fossil, suggestive of 
Dundry or of some of the Dorset beds. Another specimen in my collection is 
from the Pea-grit of Crickley. This is much smaller, and altogether more repre- 
sentative of C. Prattii, as far as one can judge of that species. 
Genus—Arvarurus, Gabb, 1869. 
The bulk of the smooth ‘ Monodontas’’ remain to be described, and the 
question for consideration is—under what genus? Monsieur Cossmann, in his 
excellent memoir on the ‘ Bathonian’ in France, adopted the genus Ataphrus. He 
attached much importance to the presence of a columellar furrow in the species 
thus classified by him. Certainly, in the majority of the smooth “ Monodontas ”’ 
