GASTEROPODA. 15 
Prerocera Bentiryi. Plate III, figs. 15, 15a, var. fig. 16. 
P. Testé turritd, anfractibus convewis, costis transversalibus (4); anfractu ultimo per- 
magno, et costato; labio externo palmato digitis quinqgue divaricatis ; canali obliquo elongato. 
Shell turrited, turbinated, whorls convex, costated, cost (4) transverse, last whorl very 
large and costated, the cost terminate in an expanded palmated wing, digitations five in 
number, beneath which are numerous diverging lines which connect the wing with the 
caudal extremity. 
The whorls are oblique in their upper and cylindrical in their lower portions; their 
encircling ribs are unequal and irregular; no other markings are preserved ; but the con- 
dition of the specimens is scarcely so good as could be wished. ‘The wing is enormously 
expanded ; the spines extend a little beyond the connecting portions of the wing. 
Locality. The Stonesfield slate at Collyweston has furnished the present specimens. 
The specific name in compliment to John F. Bentley, Esq., of Stamford, who has enriched 
our knowledge of the fossils of that locality. 
Auarta. JVov. Gen. 
A. Testé turritd, alatd et caudatd, ald integra vel digitata, interdum varicem formant; 
canali posteriori nullo, labro sinistro tenui, nunquam calloso nec anfractum ultimum obti- 
genti, labro dextro interdum ultra anfractum ultimum eatenso, canali anteriort producto aut 
breviusculo. 
Shell turrited, winged, and with a caudal extremity, wing entire or digitated, sometimes 
produced into a thickening or varix, no posterior canal, left lip thin, never thickened, nor 
extended upon the penultimate whorl, right lip sometimes extended slightly upon the 
penultimate volution, anterior canal either produced and lengthened or short. 
This genus is constituted to receive a numerous group of winged shells, which are 
separated from the true Strombidee, Rostellarize, and Pteroceree by a simple but important 
distinctive character, viz. the absence of a posterior channel upon the spire. ‘The greater 
number of our Great Oolite species of Strombidee will be found to range themselves 
under this division of the family; the character of the wing is various, consisting either of 
a simple, undivided, and thickened process, or divided into two or more digitations ; the 
channel, likewise, may be either short and straight, or lengthened and curved ; the ner 
lip is always thin—usually effuse and scarcely visible, but never produced into a thickened 
posterior ridge, as in the true Rostellariz ; the wing, in some instances, is extended slightly 
upon the penultimate volution, which is its utmost limit. 
Another character of some importance, first noticed by Mons. Deslongchamps, and 
which appears to characterise this group of shells, is this: the animal, after having 
developed the right margin of the shell, continued to increase in growth, and (like the 
species of Murex and Ranella) reproduced a second dilated and digitated margin, similar 
