PROSOBRANCHIATA. 223 
The present species is an intermediate form between P. crassicosta and P. dentata ; 
but the thick, rounded, distant ribs, the crowded transverse ornamentation, and 
the broader and shorter canal, render it easily distinguishable. 
Stze— Axis, 1 inch and 5-12ths nearly (35 millem.); diameter, half an inch (13 
millem.). The French shells attained a somewhat larger size. 
Localities—Bracklesham Bay; Bramshaw. rench—Monneville (fide Desh.), 
Aumont, Acy-en-Mulcien (fide D’Ord.). It is very rare in England, but, apparently, 
common in the French beds. 
No. 148. PLheurotoma ExorTA, Solander. Tab. XXVI, fig. 12 a, 4. 
Murex Exortvs, Sol. 1766. Brand., Foss. Hanton., p. 20, fig. 32. 
Prevrotoma ExorTA, Sow. 1816. Min. Conchol., vol. 1i, p. 104, t. 146, fig. 2. 
a — Morris. 1843. Cat. Brit. Foss., p. 157. 
— — Sow. 1850. Dixon’s Geol., &., of Sussex, p. 102. 
— — D’Orb. 1850. Prod. de Paléont., vol. ii, p. 359, No. 408. 
Nec Prevrotoma Exorta, Nyst. 1835. Recher. sur les coq. foss., &c., d’Anvers, p. 28, No. 27. 
nec _ — De Kon. 1837. Descr. des coq. foss., &c., de Basele, Boom, &c., p. 22, 
No. 21. 
nec —_— — D Orb. 1850. Prod. de Paléont., vol. ili, p. 13, No. 195 m. 
P. testd elongato-fusiformi, turritd, undique spiraliter lineaté: spird elevatd, sub- 
conicd, nodulosd : anfractibus convexis, prioribus obscure costellatis ; ultimo anfractu sub- 
conico scilicet sensim attenuato, in canali longiusculo exeunti ; marginibus posticis declivis, 
cavatis, ad suturam incrassatis, transversim exilissime lineatis ; striis spiralibus nonnullis 
remotiusculis, eminentioribus, acutis ; ceteris subtilissimis equalibus : apertura lanceolata ; 
labro valde arcuato, tenui ; sinu lato, in margine collocato. 
Shell elongated, fusiform, turreted, ornamented with spiral raised lines; the spire 
elevated and terminating in a small pointed pullus formed of two or three smooth 
volutions: whorls convex, the earlier ones very broadly and obscurely ribbed, giving a 
nodulous aspect to the spire; the posterior margins are somewhat thickened on the 
sutural edge, and but slightly depressed, so that the spire presents a nearly conical form ; 
the space between the suture and the shoulder is channeled and covered with very 
fine and regular concentric lines, so slender as scarcely to be visible by the naked eye 
or to detract from the smoothness of the surface. On the middle and front parts of 
the whorls, some of the spiral lines, rather distant from each other, are sharp and 
elevated; the rest, which cover the intermediate spaces, are very fine, close-set, 
and regular, although somewhat unequally prominent. The aperture is lanceolate, 
and terminates in a moderately long canal, gradually diminishing in width, and thus 
