PROSOBRANCHIATA. 225 



oblongo-ovali, in canali 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. 



Size. — The dimensions of 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. 150. Pleurotoma crassi-costa, F. E. Edwards. Tab. XXVI, fig. 10 a, b. 



P. testa elongato-fusifornii, angustd, turritd, costatd, undique spiraliter lineatd ; spird 

 elevatd ; anfractibus convexiuscidis, 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, inaqualibus, nonnullis eminentioribus fortibus, ceteris exilibus : 

 aperturd oblongo-ovatd ; labro leviter arcuato ; sinu lato, fere semicirculari, in margine 

 collocato. 



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- 



