GASTEROPODA. | UPPER PAL-KOZOIC MOLLUSCA. 585 
PLATYSCHISMA OVOIDEA (Phill. Sp.) 
Ref. and Syn. = Pleurotomaria ovoidea Phill. Geol. York. Vol. II. t. 15.f. 27. 
Dese.—Obliquely suboyate ; base subtruncate, convex, very obtusely rounded into the small umbilicus ; 
spire of about five very rapidly enlarging, imbricating, only slightly convex whorls; the sutures very slightly 
indented ; apical angle 100°; surface very smooth; mouth elongate ovate. Width of small specimen eleven 
lines, proportional height ;;, height of mouth and last whorl 7, between last and penultimate sutures 4, 
width of mouth #4, width of umbilicus =. 
Like most of the other species of Platyschisma the surface is so extremely smooth that it is almost 
impossible to detect the lines of growth ; when seen, however, they are in accordance with the very oblique edge 
of the mouth, much inclined obliquely, and with a slight shallow sinus, corresponding with the most prominent 
part of the surface near the base. This is considered a variety of the P. helicoides by M. de Koninck, but, 
as far asI have seen, I agree with Prof. Phillips in thinking them distinct ; that species being globose, the middle 
of the body-whorl being the most convex portion, the whorls of the spire are convex in the middle, and conse- 
quently the sutures form distinct re-entering angles, much indenting the profile. In the present species, on the 
contrary, the general form is more conoidal ; the whorls flattened, or only slightly convex, the sutures imbricating, 
and the most prominent part of the body-whorl close to the base. 
Position and Locality—Rare in the lower carboniferous limestone of Poolwash, Isle of Man. 
PLATYSCHISMA TIARA (Sow. Sp.) 
Ref. and Syn. = Turbo tiara Sow. Min. Con. t. 551. f. 1.; Phill, Geol. York. t. 13. f. 9. 
Dese.—Globose, conoidal, apical angle about 95° (but cannot be given with certainty); turreted spire of about 
six or seven gradually-increasing whorls ; whorls very tumid towards the sutures, which are thus rendered broadly 
canaliculate, the most tumid sutural portion of the whorls being crowned by a row of large, obtuse, obliquely- 
elongate nodules, extending with a slight forward direction rather more than half-way across the whorls of the 
spire, and a proportional distance on those of the body-whorl (about fourteen nodules on half a whorl at two inches 
and a half in diameter; about eleven in the same space at one inch and a-half in diameter) ; base of body-whorl 
flattened, moderately convex; umbilicus deep, rounded ; space between the coronated sutural edge and the peri- 
phery and the corresponding part of the spiral whorls moderately convex and sloping outwards. Surface smooth 
and even below the nodules. Diameter two and a half inches, proportional height %, height of mouth %, 
width of mouth about the same, diameter of umbilicus ;%, height of penultimate whorl *. 
From the structure of the mouth, the outer lip, umbilicus, and smooth shell, I incline to place this species 
in the genus Platyschisma, to which it is certainly more allied than to Turbo. The large nodules are not 
solid as in Zwrbo, but are merely modelled by an inflexion of the shell. 
Position and Locality——Rare in the lower carboniferous limestone of Kendal, Westmoreland. 
Genus. TURBO. See page 295. 
TurBO? BISERIALIS (Phill. Sp.) 
Ref. and Syn. = Turbo biserialis Phill. + T. semisulcatus Phill. Geol. York. Vol. II. t. 13. f. 10, 11. 
= Litorina biserialis de Kon. Anim. Foss. Bel. t. 40. f. 6. 
Desc.—Ovato-conic ; apical angle about 70°; spire of four gradually increasing, moderately convex whorls, 
slightly flattened in the middle ; sloping rather rapidly to the sutures, which are sharply marked ; base of body- 
whorl abruptly rounded ; a row of strong, subequal, compressed, obliquely elongate tubercles (about fourteen to 
each whorl) on the upper or sutural edge of the whorls, those of the spire extending rather more than half way 
across the space between the sutures; faint extensions from those of the body-whorl rise abruptly on the most 
convex part of the base into a second row of tubercles, similar to those near the sutures; surface with incon- 
[Fase. 111.] 3Z 
