240 EOCENE MOLLUSCA. 
No. 161. PLEuRoToMA DEsmiIA, Ff. /. Edwards. Tab. XXVIL, fig. 5. 
P. testa elongata, fusiformi, tuberculatd, spiraliter fasciolatd et lineaté: spird sub- 
conicd, valde producta : anfractibus conveais, sub-angulatis, longitudinaliter plicatis ; mar- 
ginibus posticis depressis, concavis, concentrice lineatis, ad suturam cingulo duplici, 
distanter plicato, cinctis ; ultimo anfractu repente coarctato, incanali breviculo exeuntt : 
fasciolis numerosis, antice simplicibus, ceteris inequalibus, nonnullis majoribus, crasse 
granulatis, cum aliis minoribus simplicibus, alternantibus: apertura ovali; labro valde 
arcuato, intus plicato ; sinu lato, sub-trigono, in margine collocato. 
Shell elongated, fusiform, tuberculated, and ornamented with concentric bands 
and raised lines; the spire rather thick, nearly conical and much elevated, almost 
equalling two thirds of the whole shell in length: the whorls short, convex, and 
obscurely angulated at the shoulders, where they present a double row of small, 
transverse tubercles; the posterior margins much depressed, hollowed out, and con- 
centrically lined along the middle, and bordered round the suture by a double line, 
distantly and obliquely plicated by the lines of growth of the sinus, which are very 
prominent over the whole width of the margin; the last whorl is suddenly contracted 
in front, and terminates in a rather short and narrow canal, widely notched at the 
anterior extremity. The spiral bands over the middle and front parts of the whorls 
are divided with much regularity into rows of coarse, oblong granulations, placed 
nearly below each other in an oblique direction, following the curve of the outer lip, 
and giving an appearance of plication to the whorl: the rows of granulations, which 
are separated by thickish, raised lines, rounded on the surface, diminish in size towards 
the front part of the whorls, until, on reaching the canal, they barely exceed the 
intervening lines in size, and the granulations become nearly obliterated. The 
aperture is of an oval form; the outer lip much arched, projecting in front, and _pli- 
cated within; and the sinus, which is placed rather towards the front of the margin, 
is wide, moderately deep, and sub-trigonal in form. The columella is slightly curved, 
and presents in front, at the anterior extremity, a conspicuous crest or comb. 
The present species, in the young state, somewhat resembles P. microdonta, but 
the shell is narrower, the spire relatively longer, and the canal shorter; the regular 
granulations which characterise the concentric ornamentation also render it easily 
separable. It is apparently confined to the middle eocene formations of Barton, where 
it is not uncommon. 
Stze.—Axis, 1 inch and 8-12ths, nearly ; diameter, half an inch. 
