292 BRITISH PALALOZOIC FOSSILS. [GasTEROPoDA. 
the upper half of the whorl is steeply inclined and slightly concave to the large angulation, or keel, which is 
bounded by two thread-like ridges, and is a little nearer the lower suture than the upper; lower part of each 
whorl nearly vertical, or slightly inclined inwards; strize inconspicuous, vertical on the prominent upper 
margin of the sutures, thence arching gently backwards to the keel, beneath which they take a slight forward 
curve ; base convex, with delicate spiral, thread-like strize, and a shallow imperfect umbilicus. Length about 
one inch three lines, proportional width ;;,, length of last whorl =. 
Position and Locality.—In the greenish Bala schists of Llyn Ogwen, N. Wales, and Cyrn-y-Brain, six 
miles W. of Wrexham, Denbighshire ; casts shewing no spiral strize, and shewing a variety approaching P. 
subrotundata (Portk.) in the green Bala slates of Bala, Merionethshire. 
PLEUROTOMARIA UNDATA (So7.) 
Ref.—ld. Sow. Sil. Syst. t. 8. f. 13. 
Sp. Ch.—Obtusely conical; apical angle 70° to 65°; about four and half obtusely rounded whorls, most 
prominent about their lower third, beneath which, close to the suture, is an obtuse, small keel ; sutural angle 
60°; upper part of the whorls with broad obsolete waves, extending obliquely backwards from the suture towards 
the keel; base smooth, convex, umbilicate. Total length three inches four lines, proportional length of last 
whorl &, width # (usually smaller). 
The keel and markings are often effaced and the casts are even and smooth, but retain their proportions. 
Position and Locality—Common in the green mudstone (Lower Ludlow) of Green Quarry, Leintwardine, 
Shropshire. 
Genus. MURCHISONIA (@Arch. and Vern.) 
Gen. Char.—Shell elongate, spiral, of numerous gradually increasing convex or angulated whorls; aperture 
longer than wide, rounded in front, with a deep narrow sinus in the outer lip, from whence a defined linear sinal 
band exends along the whorls of the spire. 
This genus only differs apparently from Pleurotomaria by its elongate, slender, turriculate form. 
MurcuHisonia ANGUSTATA (fall). 
Ref.—ld. Hall, Paleontology of New York, t. 10. f. 2. 
Sp. Ch.—Very elongate, subulate ; apical angle 20°; spire of about nine gradually increasing whorls, the 
lower ones obtusely angulated in the middle. Length about five lines, proportional length of last whorl =, 
width =. 
This seems to agree precisely with the species above quoted, from the ‘ Bird’s-eye limestone ” of New York, 
lying immediately over the chazy limestone near the bottom of the lower Silurian, or Cambrian system of 
New York. 
Position and Locality—tIn the concretionary ‘“chazy limestone” of Knockdollian, three miles from 
Ballintrae, Ayrshire. 
MURCHISONIA CANCELLATULA (M°Coy). PI. 1. L. fig. 20. 
Sp. Ch.—Conic, apical angle about 50°; spire of four whorls, obtusely angulated a little below the middle ; 
the part above the keel oblique, slightly convex near the sutures, slightly concave near the keel; portion below 
the keel convex ; body whorl of moderate size; base apparently imperforate (but imperfectly seen), mouth, 
obscurely rhomboidal, a little wider than high. Length one inch two lines, proportional width 3, height of 
body whorl 4; entire surface above and below the keel reticulated by nearly equal spiral and backward curved, 
oblique, transverse sulci, eight or nine in one line. 
Mr Salter, on a casual examination of some of our specimens of this species, supposed them to belong to his 
