524: BRITISH PALAXOZOIC FOSSILS. [GastERopopa: 
sinus, the angles being separated by a slight lobe (not reaching nearly to the plane of the lateral margins), 
the cicatrix of each leaving a slight sulcus extending to the beak, the space between the converging pair of 
sulci being convex; beak small, conoidal, depressed, almost overhanging the posterior margin; profile gently 
arched from the beak to the anterior margin; greatest depth considerably in front of the beak, nearly in the 
middle of the length ; sides flattened, left one more steeply sloped than the right ; longitudinal middle third from 
the beak to the front margin obtusely rounded. Shell of moderate thickness, nearly smooth, or marked with very 
minute concentric wrinkles of growth. Length one inch three lines, proportional greatest width ;,, from beak 
(shell absent) to anterior end ;4, depth #4. Muscular impressions reach to within ;; (of the length) of the 
anterior end. 
The beak being slightly within the margins, according to my measurements, instead of being terminal, 
as said by Phillips, or overhanging, as said by de Koninck, is probably due to the absence of the shell on that 
part of our specimen. 
Position and Locality —Rare in the carboniferous limestone of the Isle of Man. 
14th Family. HALIOTID. See page 290. 
Genus. PLEUROTOMARIA*. See page 291. 
PLEUROTOMARIA ALTAVITTATA? (A/°Coy). PI. 3. H. figs. 9, 10. 
Ref. and Syn.—? M*Coy, Synop. Carb. Foss. Irel. t. 5. f. 11. 
Desc.—Obtusely conical, broad-ovate, spire of four rapidly increasing whorls, and either depressed or 
moderately elevated ; apical angle varying from 150° to about 100°; whorls flattened, slightly convex above, 
sloping inwards and moderately convex below; the angle, which is situated in the upper third of the spiral 
whorls and upper fourth of the body-whorl, is very obtusely rounded, and bears the broad flattened keel on its 
upper or spiral aspect, so that it is at or slightly above the middle on the spiral whorls, and slightly above the 
most prominent part of the angulation of the body-whorl; surface nearly smooth, with obtuse, slightly irregular 
lines of growth, curving backwards to the keel on the upper portion, slightly forwards and then downwards on 
the lower portion of the whorls; on very old specimens a few, obscure, distant, spiral ridges appear on the body- 
whorl, most distinct towards the base or anterior end ; no umbilicus. Width of average specimen one inch four 
lines, proportional height = (of rather elevated variety), proportional height of mouth ;;, height of penultimate 
whorl ;*. Proportions of depressed variety, width one inch four lines, proportional height ,{;, height of mouth 
“, height of penultimate whorl =. 
This species almost exactly resembles the Plewrotomaria tumida of Phillips, as figured in the Mineral 
Conchology, t. 640, in general form, band, striation, and the appearance of spiral ridges at the base ; but in all 
the varieties the upper part of the whorls is more flattened, the band is broader, and the species is remarkably 
distinguished by the great height at which the band is placed; in the P. ¢wmida it is so low as to be entirely 
concealed by the sutures on the spiral whorls; while in the present species it is placed in the middle of the 
spiral whorls, rather nearer to the upper or posterior than the lower or anterior suture. I only put a mark of 
doubt to my reference to this species, on account of the great comparative size of the English ones, and the 
appearance of obscure spiral ridges on the base of very old examples. The general form strongly recals the 
undetermined Janthina, figured in the Geology of Russia, t. 23. f. 14. In young specimens half an inch long 
there is a trace of a very minute umbilicus. 
* M. de Koninck calls the anterior parts of these shells, the superior, contrary to the custom of most writers. I 
have described them in the old and more natural way as cones with the base downwards, and calling the apex (or posterior 
end), and parts near the apex, upper, and parts near the base or mouth lower. 
