356 GASTEROPODA OF THE INFERIOR OOLITE. 
N.B.—The figured specimen does not exhibit these latter features distinctly. 
Relations and Distribution.—This very commonplace little shell seems to differ, 
as far as I can judge, from any species in the Inferior Oolite, though it may 
resemble some of the smooth Turbos recognised in the Lias. Notwithstanding 
the absence of any well-defined denticle, the character of the aperture rather 
reminds one of Ataphrus. 
Not very uncommon in the ‘‘ Base-bed” at Lincoln. 
Grour IL.—Sculptured Shells. 
One of the most difficult problems which present themselves for solution in 
Jurassic paleontology is the correct generic classification of the numerous members 
of the Turbinide coming under Group II. Except as regards the genus Tvochus, 
which is undoubtedly represented in considerable numbers, the identification of the 
modern genera, Monodonta, Turbo, Delphinula, &c., is to acertain extent empirical. 
I have always had an objection to the acceptance of Monodonta, but there is safety 
in Turbo as a general term, which may be held to include various sections by some 
recognised as distinct genera. Delphinula, too, has had its advocates, and many 
species of Jurassic Turbinide have from time to time been thus classified. lifes 
then, I continue to use the genus Monodonta for Jurassic shells, it is only in a 
conventional sense, as Turbo would do just as well. For the same reason no 
diagnosis is offered either of Monoponta, Turso, or DELPHINULA. 
291. Monoponta pisouitica, sp. nov. Plate XXIX, fig. 17 and P fig. 18. 
Description : 
Height ‘ : : j . 4mm. 
Width : P : : . oso. mm. 
Spiralangle . : ‘ 2 Go:; 
Shell trochiform, thick, imperforate; apex rather obtuse, spiral angle regular. 
Number of whorls about five; the apical ones are smooth and round, the remainder 
flat, and ornamented by four tuberculated spirals, which in the body-whorl present 
some differences, the anterior spiral at the angle of the shell having larger 
granulations than the others. Body-whorl subangular and rather more than half 
the total height ; base full, and ornamented with granulated spirals rather finer 
than those at the sides. Outer lip circular; columella nearly straight, and reflexed 
