328 GASTEROPODA OF THE INFERIOR OOLITE. 
and in the lower zones of the Inferior Oolite in Dorset, especially at Bradford 
Abbas. Rare at Duston. 
The two species next described are closely related, and indeed Onustus 
acuminatus 18 little more than a variety. 
260. ONUSTUS ACUMINATUS, sp. nov. Plate XXVII, fig. 3. 
Description : 
Height restored : ' : .) S22aro: 
Width : : : . 26mm. 
Opening of spiral angie : : . 40°. 
Mean spiral angle : 75°. 
Shell pyramidal, imperforate ; spiral angle extremely concave. Number of 
whorls about nine ; the apical whorls are flat, but with the increase of the spiral 
angle become much more excavated, so much so that the spire seems as if it 
scarcely belonged to the three anterior whorls. ‘The ornaments are similar to 
those in some of the varieties of O. pyramidatus, the coste being fully developed 
to the very edge of each whorl. The base is flat, smooth, or with slight radial 
lines of growth, and there is scarcely any trace of an umbilical excavation. 
Relations and Distribution.—This form exhibits the concave spiral angle to a 
far greater extent than any species of Onustus in the Inferior Oolite of this 
country, in this respect somewhat resembling Onustus papyraceus, Héb. and Desl., 
from the Callovian of Montreuil-Bellay. It is quite possible that where the spire 
has been lost there are no means of distinguishing O. acwminatus from the more 
common 0. pyramidatus. 
Rare in the Murchisone-zone at Bradford Abbas, and probably occurring on 
the same horizon at one or two other places in North Dorset. There are two 
specimens from the Inferior Oolite of Nailsworth, now in the Jermyn Street 
Museum, which may be referred to O. acuminatus. 
261. Onustus, species or variety. Plate XXVII, figs. 5a, 5b. 
Description : 
Height : : : ' . 16mm. 
Width : i ‘ : . 23 mm. 
Spiral angle . , ‘ : fh G2. 
