5384 BRITISH PALALOZOIC FOSSILS. [GASTEROPODA. 
slightly convex whorls ; body-whorl very obtusely rounded at the periphery ; base moderately convex; mouth 
very oblique, considerably wider than high ; umbilicus small, rounded ; sutures slightly imbricated, inconspicuous, 
forming a fine impressed line, deepest towards the apex ; surface very smooth. Diameter of large specimen two 
inches, proportional height ;4, height of last whorl ;{;, from suture of last, to suture of penultimate whorl 4, 
width of mouth “, width of umbilicus =. 
It is almost impossible to detect the lines of growth of this species, the surface is so very smooth; 
they are, however, very oblique, and with a very faint backward wave at the periphery. M. de Koninck con- 
siders this species a mere variety of P. helicoides, but of the many specimens of both species which I haye 
examined none seem to be intermediate in apical angle. 
Position and Locality —Common in the lower carboniferous limestone of Kendal, Westmoreland. Several 
very small specimens (from one to four lines in diameter), apparently the young of this species, from the lower 
limestone of Lowick, Northumberland. 
PLATYSCHISMA HELICOIDES (Sow. Sp.) 
Ref. and Syn. = Ampullaria (and Globulus) helicoides Sow. Min. Con, t. 522. f. 2 (left-hand figure). 
Desc.—Globose, profile of spire slightly convex ; tangents to the penultimate whorl giving an apical angle 
varying from 87° to 105°, very rarely the former, most usually 100°, the obtusely depressed apex not reaching to 
this angle; spire of six gently convex whorls; sutures very delicately marked simple lines ; surface extremely 
smooth, polished; periphery very obtusely rounded; base very tumid, rounded; umbilicus small, rounded ; 
mouth slightly longer than wide. Width of average specimen one inch two lines, proportional height “, 
height of last whorl 4, from last to penultimate suture %, width of umbilicus about 2%. 
From the extremely glabrous surface it is almost impossible to detect the lines of growth ; the edge of the lip 
seems, however, to have been gently sigmoid and oblique. Our specimens do not shew the spiral striation said 
to mark the edge of the umbilicus, probably from the absence of the outer shell on that part. 
Position and Locality.—Common in the impure lower carboniferous limestone of Lowick ; not uncommon, 
of small size, in the carboniferous shale of Craige, near Kilmarnock. 
PLATYSCHISMA JAMESI (M/*Coy). 
Ref.—M°Coy, Syn. Carb. Foss. Irel. t. 5. f. 20 (strize and tumidity of suture slightly too strong). 
Desc.—Conical, very depressed when young, becoming more elevated and acute with age, the tip of the 
spire always remaining obtuse ; apical angle 140° at three lines in diameter, 100° at five lines in diameter, and 
95° at the adult diameter of eight lines; spire of six flat, imbricating, gradually increasing whorls, the edges of 
the sutures slightly thickened, and the lower part of each whorl slightly rounded obtusely into the sutural line ; 
base flattened, sloping gradually to the small, rounded umbilicus ; periphery obtusely rounded. Surface with very 
fine, oblique, obtuse, unequal, inconspicuous lines of growth, having a slightly sigmoidal flexure, indicating 
a convexity in the outer lip at the upper or posterior end, and a shallow backward wave at the circumference of 
the body-whorl seen just above the sutures of the spire. Diameter of adult specimen eight lines, proportional 
height of the same ¥, height of mouth #4, distance between last and penultimate sutures =, width of mouth 
iw» Width of umbilicus =; ordinary sized young specimens five lines in diameter have a proportional height of 
only wh: 
This species is remarkable for the great and regularly progressive difference of the apical angle with the 
age or size of the individual. 
Position and Locality—Common in the lower carboniferous limestone of Kendal; in the carboniferous 
limestone of Malham Moor. 
