438 — GASTEROPODA OF THE INFERIOR OOLITE. 
Shell conical, turrited, only slightly umbilicate. Spire regular and sharp, 
except just at the apex, where it is rather flattened. Whorls in a medium-sized 
specimen seven, angular, the posterior third having a moderate slope, and the 
anterior two-thirds being nearly vertical ; sutures close and not canaliculate. The 
keel of each whorl carries a coronet of undulating tubercles, and the whole shell is 
pervaded by fine and close undulating spiral ornament, which is decussated by 
extremely fine radial lines. 
The sinus-band is wide, flat, and submedian, with spiral striz decussated by 
growth-lines, and this kind of ornamentation is continued throughout, except in 
the body-whorl of very large specimens. The body-whorl is large and biangular ; 
the lower keel, or basal periphery, is scarcely tuberculate, and in very large 
specimens almost smooth. The base is flat-convex with extremely fine reticulate 
ornament; the umbilicus is small and inconspicuous, but rather deep in some of 
the younger forms. Aperture square to subcircular. 
Relations and Distribution.—In Pl. intermedia, Mimster (Goldfuss, pl. elxxxi, 
5), which is said to occur in the Lias, we have in many respects a very similar 
shell; but in that species the sinus-band is represented as occurring on the 
keel. Pl. subaraneosa is little more than a modified form of Pl. araneosa, var. 
reticulata, Deslongch. (vol. cit., p. 89, pl. xiv, fig. 5), thus affording another 
instance of a Liassic survival. Our shell, however, is rather more subdued in 
ornaments and presents some minor points of difference; which facts, coupled 
with its comparative abundance in the Concavus-bed at Bradford Abbas, seem to 
entitle it, provisionally at least, to be regarded as a distinct species. 
At Bradford Abbas the majority of the specimens are immature, consisting of 
about five or six whorls. ‘The fine and close reticulate ornamentation is well 
exhibited in some of these, and there is a specimen from the same horizon at 
Beaminster where the close and delicate spiral system in the base is well brought 
out. On the other hand, the base of the larger specimens appears smooth (? from 
wear). Individuals with eight whorls attain to a large size (basal diam. 80 mm.). 
In these the umbilicus is almost closed, and the shells present the appearance of 
having been worn. ‘here is a specimen from Dundry, in Mr. Wilson’s Collection, 
where the ornamentation in the spire is bolder (or better preserved), and this still 
more nearly resembles Pl. araneosa. 
In this connection, also, I would draw attention to a specimen (Pl. XX XIX, 
figs. 2a, b) from the Liassic Sands of Gloucestershire, where the ornamentation is 
bolder than in Pl. suwbaraneosa, and altogether more like that of Deslongchamps’ 
species. N.B.—The actual specimen does not warrant the amount of umbilicus 
shown in the figure. 
Secondly, there remains for consideration the large species of Plewrotomaria 
occasionally found in the lower part of the Yorkshire Dogger, and identified by me 
