GAsTEROPODA. | UPPER PALAZOZOIC MOLLUSCA. 533 
Genus. POLYTREMARIA (D’Orb.) 
Gen. Char.—Form and general characters as in Plewrotomaria proper, but the band constricted at short 
intervals, so as to form a row of approximate, oval foramina, as in Haliotis, the last ten or twelve of which 
commonly remain open. 
POLYTREMARIA CATENATA (de Kon. Sp.) 
Ref. and Syn. =Pleurotomaria catenata de Kon. Anim. Foss, Belg. t. 32. f. 1. = Polytremaria catenata 
(de Kon.) d@Orb. Prodrome, p. 122. 
Desc.—Spire conical; apical angle about 80°; of about six whorls, each strongly angulated a little 
above the middle; the part above the angle slightly concave, sloped, or nearly horizontal; the part below 
the keel flattened and nearly vertical; base rounded; umbilicus very small; mouth rotundato-quadrate ; 
surface strongly marked with coarse, unequal, spiral, thread-like strize, about three or four above the keel, and 
four or five below it on the penultimate whorl, about the same size, and covering the base of the body-whorl, 
crossed by fine strize of growth, oblique above the band, nearly vertical below it ; band thick, the transversely 
oval apertures numbering about sixteen in each turn. Length about eight lines, proportional width {;, height 
of last whorl #5, height of penultimate whorl ;;. A specimen five lines long has the proportional width >. 
M. de Koninck’s figure is rather broader at the base, has the band lower, and the yolutions more rounded 
and less angulate than in our examples, or in his description. The proportional width seems to increase 
with age. 
Position and Locality.—Rare in the impure lower limestone of Lowick, Northumberland. 
Genus. PLATYSCHISMA (d7°Coy) 1844. 
Ref.—Synopsis Carb. Foss. Irel. 
Etym.—Maris, wide; and cx}, a slit. 
Gen. Char.—Obtusely conical, ventricose ; spire short, obtuse, of few whorls; aperture very oblique, large, 
lunate, deeply indented by the preceding whorl, rounded anteally, narrow retrally ; with a very wide, shallow sinus 
in the middle of the outer lip, not forming a defined band, and sometimes obsolete; no trace of inner lip; pillar 
thin, a little reflected ; surface smooth, or only marked by the retrally waved lines of growth ; umbilicus small, 
rounded, open. 
This group of shells is very distinct from Plewrotomaria (with which they have been classed by most 
writers) in several important characters, of which the want of a definite mesial band is the most striking; they 
are also recognized by their obtuse form, smooth surface, without keels of any kind, the great width, obliquity, 
and shallowness of the sinus, as indicated by the lines of growth, which are sometimes even nearly straight, 
and the comparative thinness of their shell. They resemble the recent Janthinw strongly in general shape 
and striation, but differ from them in the thickness of the shell, in having the mouth rounded anteally 
instead of being angulated, and not haying the pillar lengthened as in that genus. From S#raparollus 
(with which many of them are grouped by d’Orbigny, &c.) they differ by their fewer whorls, greater obliquity of 
outer lip, and total absence of inner lip. They seem most allied to Sigaretus, and might probably with 
advantage be placed in the same family, instead of near Sfomatia in the present one. The species appear con- 
fined to the carboniferous limestone. 
PLATYSCHISMA GLABRATA (Phill. Sp.) 
Ref. and Syn. = Pleurotomaria glabrata Phill. Geol. York. t. 15. f. 28. 
Dese.—Discoid, or obtusely lenticular, much depressed ; profile of spire convex from the depression of the 
apex; tangents to the middle of the outline on each side give the apical angle of 130°, which from the depres- 
sion of the apex would be much larger in young specimens; spire very obtuse, of six gradually increasing, 
