372 GASTEROPODA OF THE INFERIOR OOLITE. 
The small variety figured in the accompanying plate is characteristic of the 
Opalinus-zone of Drympton and Haselbury, and probably of other localities. Some 
specimens more conical than the one figured I distinguish in my collection as var. 
conica. There is also a large variety in the Murchisonx-zone of Burton Bradstock 
which comes very near to 7’. Sedgwicku, Mimst. It is just possible that a modifi- 
cation of this species—or species-group—from the Dogger is represented in ‘ Geol. 
Mag.,’ 1885, pl. u, fig. 13. 
309. Trocnus Winwoontl, Tawney, 1873. Plate XXXI, fig. 4 (minor), fig. 5 (major). 
1873. Trocuus Winwoont, Tawney. Dundry Gasteropoda, p. 34 (26), pl. ii, fig. 8. 
Bibliography, §c.—This species was based upon a single specimen in the 
Bristol Museum, the locality being uncertain. The author observed that there 
was some resemblance to Quenstedt’s figure of Tvochus bijugatus (‘ Der Jura,’ p. 
485, pl. Ixv, fig. 9). Since the year 1873, analogous if not positively identical 
forms have been found abundantly in the Concavus-bed at Bradford Abbas, where 
the species exhibits great variety. The form is probably derived from the more 
conical varieties of the Sandersii-group, which is, in the main, characteristic of a 
lower horizon. 
Description, var. minor : 
Height . : : : =~ 2) mams 
Basal width . : : P 5 1S) iaataal, 
Spiral angle . : : 47° 
Shell regularly conical, elevated, more or less umbilicated. Spire acute and 
occupying nearly two-thirds of the entire height. Number of whorls seven or 
eight; these are concave with finely tuberculated keels, not very salient, at the 
posterior and anterior margins, the intervening space being seamed with 
granulated spiral striz somewhat decussated axially ; sutures wide and regular. 
The body-whorl is similar in shape and similarly ornamented, the second 
carina forming the angle of the whorl, immediately below which, and partly in the 
base, is a third subordinate carina. The base inclines to be flat, though rising 
anteriorly, and is richly ornamented with granular spirals which are partly 
decussated by axial strize and growth-lines: a row of slight tubercles girdles the 
umbilicus, which is sometimes barely indicated. Aperture trapezoidal. 
In the variety major the ornaments are much coarser, in the whorls of the 
spire a third carina being exposed. In the body-whorl this attains to considerable 
importance, so as to produce a duplicate keel at the angle of the shell. The 
