272 GASTEROPODA OF THE INFERIOR OOLITE. 
species of Rissoina in the Inferior Oolite, viz. R. obliquata, Sow., with varieties ; 
R. obtusa, Lycett ; and hk. gymnoides, sp. noy.' 
205. Rissomna oBLiquata, Sowerby, 1829. Plate XXI, fig. 7; var. parcicostata, 
fig. 8—? var. fig. 9. 
1829. Rissorna opriguaTa, Sowerby. Min. Conch., pl. deix, fig. 3. 
1851. = — Morris and Lycett. Great Ool. Moll., part i, p. 52, 
pl. ix, fig. 19. 
1852. — “pupuicata,” d’Orbigny. Terr. Jurass., vol. ii, pl. cexxxvil, 
figs. 1—3. 
Bibliography, §e.—Originally described by Sowerby from the Great Oolite of 
Ancliff, together with F. acuta and R. duplicata. Morris and Lycett speak of it as 
rare in the Great Oolite of Minchinhampton. D’Orbigny’s figure named “ dupli- 
cata ”’ is not at all like Sowerby’s R. duplicata. The artist seems to have got 
hold of f. obliquata by mistake. 
Description : 
Length about : : : - Omom, 
Length to width as 5 4 « 1 30-45. 
Spiral angle (obtuse) about . : 28°. 
Shell turrited, subelongate, turbinate, often tage Whorls about seven, 
tumid, close, and costated ; the costz (about twelve in each whorl) are prominent, 
and curve with a slope from right to left. Aperture restricted, ovate posteriorly, 
flattened and subcanaliculate in front ; lips much thickened. 
Relations and Distribution —As compared with R. acuta this species is wider 
and stouter, the whorls are more tumid, and the coste usually more prominent ; in 
the varieties they are fewer in number. It has a considerable resemblance to the 
existing F. costata. The typical form is fairly plentiful at Weldon. 
Var. parcicostata (fig. 8). This is a stillmore stumpy form ; the coste are fewer 
in number, prominent, and less curved. This variety prevails at Great Ponton. 
Micromorphs occur there and in the Scarborough Limestone. 
Variety or sport (fig. 9). The points wherein ft. obliquata differs from R. 
acuta become intensified in this form, which is extremely stumpy and very coarsely 
ribbed. It has a length of 6 mm. and a spiral angle of about 40°. The aperture 
is strongly canaliculate anteriorly. 
A single specimen in the Sharp collection at the British Museum. We might 
call this R. obliquata, var. “ inflata,” or simply Rissoina “ inflata.” 
! Rissoina cancellata, Morris and Lycett, is quoted from the shelly beds of Ponton (Morris, 
‘Quart. Journ, Geol. Soe.,’ vol. ix, p. 326), but I can find no confirmation of this. 
