GAsTEROPODA. | UPPER PALAOZOIC MOLLUSCA. 529 
narrow outer edge, and having the sinal band along its upper flat side, bounded internally by a faint obtuse 
ridge; the whorls above the keel have a sigmoidal profile, being gently convex in the middle from the upper 
suture, and becoming concave, or curving outwards, in the lower third, to blend with the upper side of the thin 
flat keel; below the keel the whorl slopes rapidly into the suture, slightly concave near the keel, convex at 
the suture; keel rather below the middle of the basal whorl, and at one-third from the lower suture in the 
spiral whorls; base very convex ; umbilicus moderately large, open, conical, deep; mouth transversely cordate, 
angular externally ; surface almost smooth, with membranous, minutely wrinkled, or irregular strize of growth, 
slightly arching obliquely backwards to the keel; recurved on its flat upper surface, and thence extending 
almost directly into the umbilicus; a few fine spiral stria at the edge of the umbilicus, under the lens. 
Diameter of small specimens two inches nine lines, proportional height ;;,, height of last whorl x, height of 
penultimate whorl 22, width of mouth “, diameter of umbilicus 3%, projection of thin keel on body-whorl ;;; 
(occasionally six inches in diameter). 
M. de Koninck, in the supplement to his Fossils of Belgium, figures what seems the Plewrotomaria 
carinata of Sowerby as this species, apparently on the supposition that my original figures and description 
were totally inaccurate in all respects. A specimen in the University collection from Lowick, however, 
shews the smooth (not spirally sulcated) surface, and the extremely prominent, peculiar, compressed keel, 
exactly according with my original figures and description, as also a less perfect fragment from Ireland. 
Position and Locality.—V ery rare in the carboniferous limestone of Lowick, Northumberland. 
PLEUROTOMARIA HELICINOIDES (//°Coy). 
Ref. and Syn.—M°Coy, Synop. Carb. Foss. t. 7. f. 6.= Trochus subhelicinoides @Orb. Prod. p, 119. 
Dese-—Discoid, lenticular, depressed; spire very obtusely conic ; apical angle 126°, composed of four and 
half turns; body-whorl sharply carinated in the middle, the sharp projecting keel having the narrow band placed 
flatly on its upper side, defined within by a fine impressed line; this keel and band touch the simple suture on 
all the whorls of the spire, all of which shew the band distinctly ; surface of each whorl slightly concave near 
the band, and slightly convex near the upper suture; base of body-whorl depressed, gently convex ; umbilicus 
narrow, rounded. Width one inch four lines, proportional height “4, height of last whorl =, height of penulti- 
mate whorl ;°,, width of mouth 3, width of umbilicus |%, width of band about half a line. Surface apparently 
smooth. 
As the specimen in the collection was crushed, I have taken the apical angle and measurements from the 
original Irish one. I know not why M. d’Orbigny has changed the genus and specific name of this species. 
Position and Locality——Rare in the black beds of the carboniferous limestone of Derbyshire. 
PLEUROTOMARIA STRIATA (Sow. Sp.) 
Ref. and Syn. = Helix striata Sow. Min. Con. t. 171. f. 1. 
Desc.—Shell depressed, conical; apical angle about 90°; spire low, of five flattened, or slightly convex, 
rapidly enlarging whorls; periphery of body-whorl angulated; base flattened, gently convex; no umbilicus ; 
mouth transversely rhombic ; band broad, deeply hollowed, bounded by two strong prominent keels on the angle 
of the body-whorl, the lower of which is concealed by the suture on the spiral turns. Surface strongly sculptured 
with regular, simple, subequal, oblique, very slightly arched, thread-like ridges, about their own thickness apart 
above, forming arched, scale-like strize in the band, and slightly sinuous and dichotomous on the base of the 
body-whorl (about seven strize in two lines on the body-whorl). Average width one inch, proportional height ,7, 
height of last whorl =, height of penultimate whorl ;5, width of mouth ;;. 
The want of umbilicus and spiral strie separate this species from the P. carinata Sow. 
Position and Locality—Rare in the carboniferous limestone of Bolland. 
oaxeg) 
