GAsTEROPODA. ] LOWER PALAZOZOIC MOLLUSCA. 291 
notched or perforated opposite the corresponding apertures in the edge of the shell, to admit the water to the 
respiratory cavity when the animal is contracted; pectinated gills nearly equal). 
Differ from the Trochide by wanting the filaments to the foot, wanting the operculum, and by the band 
and respiratory slit or row of perforations in the shell. 
Genera :—1, Haliotis; 2, Cirrus; 3, Ditremaria; 4, Plewrotomaria; 5, Murchisonia; 6, Platyschisma ; 
7, Stomatia. 
Genus. PLEUROTOMARIA (Defrance). 
> Ptycomphalus (Ag.) 
Gen. Char.—Usually pyramidal, trochiform, more rarely globose, or depressed ; aperture usually wider than 
long, with a deep narrow respiratory slit in the outer lip, leaving a defined, linear, spiral band, marked by retro- 
flex strize along each whorl of the spire; surface usually marked by strize arching backwards towards the band ; 
columella simple, a little thickened in front, with or without umbilicus. 
The trochiform species differ from 7rochus by the sinus and band. 
PLEUROTOMARIA CRENULATA (M°Coy). Pl. 1. K. fig. 45. 
Sp. Ch.—Obtusely trochiform, length and width nearly equal; apical angle 85°; spire of four obtusely- 
round whorls, most convex below the middle ; band broad, depressed, bounded by two delicate prominent keels, 
the upper edge being a little below the middle of the whorl; a space equal to the band in width is visible below 
it on the turns of the spire; base flattened, gently convex, slightly umbilicate; surface with close, sharp, 
irregular, interrupted striz, slightly arched backwards from the spire to the suture, and in the opposite direction 
beneath it; the oblique strie faintly crenulated by very minute spiral strize, the band with coarse, irregular, 
backward-arched lines only. Length six lines, proportional width *, length of body whorl jj. 
This bears some slight resemblance to the Turbo carinatus (Sow.) of the Upper Ludlow, but is generically 
distinct by its strize arched backwards to the band ; its spire is also shorter, and there are no spiral ridges on 
the base. 
Position and Locality.—In the Upper Ludlow rock of Brigsteer, Kendal, Westmoreland. 
Explanation of Figures—P\. 1. K. fig. 45, natural size; fig. 45 a, magnified (the spiral striation not 
sufficiently distinct in this figure through a slight failure in the lithograph). 
PLEUROTOMARIA LENTICULARIS (Sow. Sp.) 
Ref. and Syn. = Trochus lenticularis Sow. Sil. Syst. t. 19. f. 11. 
Sp. Ch.—Lenticular, very much depressed, sharp-edged ; whorls only slightly convex above and below ; 
apical angle about 135°; a small sharp keel encircles the circumference of the body whorl, and exactly coincides 
with the suture of the spiral whorls; immediately above it is a moderately wide band, so slightly concave, and 
so obscurely defined, as to be scarcely visible; surface nearly smooth, under the lens (when the shell is pre- 
served) very minute close striz arch backwards from the suture to the band, where the curve is reversed, 
these strize are crossed by equally fine and close spiral strize ; umbilicus narrow, deep; diameter one inch five 
lines, proportional height about =. 
This species very rarely exhibits the true surface preserved. 
Position and Locality—In the olive schists of the Lower Ludlow rock of Green Quarry, Leintwardine, 
Shropshire ; a small, less depressed variety, in the Bala schists at Alt yr Anker, Meifod, Montgomeryshire. 
PLEUROTOMARIA TURRITA (Portk.) 
Ref—ld. Port. Geol. Rep. t. 30. f. 7. 
Sp. Ch.—Elongate, conic, turreted ; apical angle about 60°, spire of about four or five strongly angulated 
whorls ; the sutures slightly adpressed and prominent above, from a narrow subcentral keel, from whence 
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