272 
GASTEROPODA OF THE INFERIOR OOLITE. 
species of Bissoina in the Inferior Oolite, viz. B. obliquata. Sow., with varieties ; 
B. ohhisa, Lycett ; and B. gymnoides, sp. nov.^ 
205. Rissoina obliquata, Sowerhy, 1829. Plate XXI, fig. 7 ; var. parcicostata, 
fig. 8 — ? var. fig. 9. 
1829. Rissoina obliquata, Sowerhy. Min. Conch., pi. dcix, fig. 3. 
1851. — — Morris and Lycett. Great Ool. Moll., part i, p. 52, 
pi. ix, fig. 19. 
1852. — “ DUPLICATA,” d'Orhigny. Terr. Jurass., vol. ii, pi. ccxxxvii, 
figs. 1 — 3. 
Bibliography , ^c. — Originally described by Sowerby from the Great Oolite of 
Anclifi, together with B. acuta and B. 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 B. duplicata. The artist seems to have got 
hold of B. obliquata by mistake. 
Description : 
Length about . . . .6 mm. 
Length to width as . . . 1 : 0*45. 
Spiral angle (obtuse) about . . . 28°. 
Shell turrited, subelongate, turbinate, often twisted. Whorls about seven, 
tumid, close, and costated ; the costse (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. 
Belations and Distribution. — As compared with B. acuta this species is wider 
and stouter, the whorls are more tumid, and the costae usually more prominent ; in 
the varieties they are fewer in number. It has a considerable resemblance to the 
existing B. costata. The typical form is fairly plentiful at Weldon. 
Var. parcicostata (fig. 8). This is a still more stumpy form ; the costae 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 B. obliquata differs from B. 
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 B. obliquata, var. “ injiata,” or simply Bissoina “ infiata.’’ 
^ Rissoina cancellata, Morris and Lycett, is quoted from the shelly beds of Ponton (Morns, 
‘ Quart. Journ. Geol. Soc.,’ vol. ix, p. 326), but I can find no confirmation of this. 
