PROSOBRANCHIATA. 225 
oblongo-ovali, in canalt longo, angusto exeunti ; labro leviter arcuato ; sinu lato, in margine 
collocato. 
Shell long, narrow, fusiform, turreted, longitudinally ribbed, and concentrically 
lined: the spire, consisting of nine or ten volutions, is pointed, elevated, forming 
nearly a half of the length of the whole shell. The whorls are slightly convex and 
angulated at the shoulders; the posterior margins concave, slightly thickened round 
the suture, and covered with fine, thread-like, concentric lines, one or two of which 
near the edge are stronger and more prominent than the rest. The spiral lines over 
the middle and front parts of the whorls are numerous, irregular, unequal; some, more 
or less distant from each other, are prominent and sharp, and the intermediate spaces 
are occupied by two or three, occasionally by four, very slender and regular lines; the 
longitudinal ribs, which are rather numerous, narrow, and oblique, reach almost to the 
anterior canal. The aperture is oblong and ovate, and terminates in a moderately 
long, straight, and narrow canal; the outer lip is thin and slightly arched; the sinus 
wide, semi-circular in shape, and placed in the middle of the margin. 
The present species, distinguished by its long costated spire, appears to be 
peculiar to the English middle eocene strata ; Defrance, it is true, refers to it, although 
with doubt, as a synonym of P. dentata, but a slight comparison of the shells will 
prevent the two species being confounded. It presents closer resemblances as well 
to P. textiliosa, as to P. crassi-costa; from both of these species, however, not- 
withstanding the similarity in the ornamentation, it may be easily distinguished by 
the slenderer and more numerous ribs, and the longer and narrower anterior canal. 
Stze-—The dimensions cf my largest specimen are—axis, 1 inch and 4-12ths; 
diameter, 5-12ths of an inch. ‘Those of Brander’s specimen, although represented in 
the figure given by him as considerably larger, are, in fact, very nearly the same. 
Localities —Barton, Alum Bay (No. 29, Prestwich), Highcliff, Bracklesham Bay. 
No. 159. PLEuRoToMA crassi-costa, F. &. Edwards. Tab. XXVI, fig. 10 a, 0. 
P. testé elongato-fusiformi, angustd, turritd, costatd, undique spiraliter lineata ; spira 
elevatd ; anfractibus convextusculis, angustatis ; marginibus posticis latiusculis, concavis, 
tenuissime lineatis, ad suturam incrassatis, cingulo duplici ornatis ; ultimo anfractu parvo, 
repente coarctato, in canali lato, longo, subrecto exeunti ; costis distantibus, brevibus, crassis : 
lineis spiralibus confertis, inequalibus, nonnullis eminentioribus fortibus, ceteris evilibus : 
apertura oblongo-ovata ; labro leviter arcuato ; sinu lato, fere semicirculari, in margine 
coljocato. ’ 
Shell long, narrow, fusiform, turreted, ribbed, and having the whole surface orna- 
mented with concentric lines: the spire, formed of eight or nine volutions exclusive of 
the pullus, is moderately elevated and pointed; whorls slightly convex, sharply angu- 
