412 GASTEROPODA OF THE INFERIOR OOLITE. 
referred to this form further differ from the typical Pl. sulcata in having the 
sutures rather more canaliculate and the umbilicus narrower and deeper; on the 
whole, too, the shells have less ornament. In most of my specimens the sinus- 
band is flat or countersunk, and the body-whorl relatively very large. 
This is to all appearance an obconical variety of Pl. sulcata, though not 
exactly Pl. obconica, Tawney. 
The figured specimen of Tawney’s ‘ obconica,’ which must of course be 
regarded as the type, has the whorls distinetly angular, as in Pl. wnisulcata, 
dOrb. But on the very same tablet (in the Bristol Museum) is an obconical 
specimen with rounded whorls, just like fig. 7 of the accompanying plate. It 
seems only reasonable to suppose that Tawney included such a form in his 
“ obconica.” Inferentially, therefore, this variety represents Pl. obconica, Tawney, 
although the figured specimen is not exactly the same. 
Relations and Distribution.—In Dorset Pl. suleata and the obconical variety 
just described are essentially fossils of the Murchisone-zone, bemg especially 
abundant at Coker and the Irony Nodule-bed at Burton Bradstock; rarer at 
Bradford Abbas and Stoford. The exact horizon at Dundry is not known to me, 
although there is good reason to believe that it is in the Murchisonex-zone. 
This species, in common with many other Inferior Oolite Plewrotomarie, 
probably occurs in the Cotteswolds. Most specimens there are in the form of 
casts; hence the exact species is not easy to determine. 
349. Prevroromarta (Leptomaria) Asax, d’Orbigny, 1850. Plate XXXV, figs. 8, 
8a, 8b; and obconical variety, 
figs. 9, 9a. 
1850. PrevroromMarta AgaXx, d’Orbigny. Prod., i, p. 268. 
1854. oo = — Terr. Jur., vol. ii, p. 484, pl. ceelxxxvili, 
figs. 1—5. 
Description : 
Height : : 5 : = alommm: 
Basal diameter : : : . 23 mm. 
Spiral angle (convex) . 4 = 100°: 
Shell heliciform, with a narrow cinbikiouss Spire convex and depressed, apex 
very obtuse. Whorls (about six) narrow, tumid, and regularly marked with fine 
spiral strie ; these are very faintly cross-hatched in the earlier whorls, otherwise 
there is no axial ornamentation; sutures canaliculate. 
The sinus-band is narrow and sunken, marked with fine lines or plain; in the 
