296 BRITISH PALAZOZOIC FOSSILS. [GasTEROPODA. 
Turso ? WILLIAMS! (So7.) 
Ref —Id. Sil. Syst. t. 8. f. 6. 
Sp. Ch. (from casts.)—Obtusely trochiform, of about four gently convex whorls; apical angle about 90° ; 
base of body whorl rounded ; umbilicus narrow, deep; mouth oblique, ovate, a little longer than wide; surface 
apparently even. Width one inch four lines, length probably one inch three lines, length of body whorl 
eight lines. 
I cannot distinguish the specimen before me from the above species quoted by Sowerby from the Upper 
Ludlow tilestone of Horeb Chapel, in which gisement, however, it will be remarked, there are several other lower 
forms. 
Position and Locality —In the fine micaceous sandstone of Mandinam, Caermarthenshire. 
Genus. TROCHUS (Linn.) 
Gen. Char.—Shell conical, of several regularly increasing whorls, base of body whorl flattened, with the cir- 
cumference obtusely carinated ; aperture transversely oblong, wider than long, outer lip thin, oblique; colu- 
mella short, usually twisted ; with or without umbilicus ; operculum round, horny, of very numerous spiral turns. 
Distinguished from Turbo by the regular conical shape, flattened base, and transverse elongation of the 
mouth. 
Recent in all seas, herbivorous, at and below low-water mark among rocks, and in the principal groups of 
strata from the Cambrian inclusive. 
TrocHus C#LATULUS (M°Coy). PI. 1. K. fig. 40. 
Ref—ld. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 49. 
Sp. Ch.—Conical, apical angle 80°; spire of three and half flattened volutions, having a thick rounded keel 
forming the circumference of the basal whorl, and close to the suture on the spiral whorls; base flattened ; 
surface marked with oblique scaly ridges. Width four lines, proportional length 5; length of last whorl =. 
Owing to the scaly nature of the ornament on the rather wide, oblique ridges of the surface, they 
usually adhere to the matrix, and breaking off from the shell leave it nearly smooth. 
Position and Locality —Very rare in the limestone of Old Radnor, Radnorshire. 
Explantion of Figures —PI. 1. K. fig. 40, natural size; fig. 40 a, magnified. 
Trocuus constrictus (M*Coy). Pl. 1. K. fig. 41. 
Ref.—ld. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. p. 50. 
Sp. Ch.—Conical, apical angle about 70°, of four or five gradually increasing whorls, each with a shallow 
concavity or constriction below the suture, the lower portion strongly rounded, base flattened, circumference 
obtusely rounded; surface obliquely crossed by fine, unequal, often obscurely fasciculate lines of growth; 
mouth transverse, obliquely ovate. Length eight lines, proportional width =; length of mouth 7%, width of 
mouth =. 
This seems allied to the Holopea symmetrica (Hall) of the Trenton limestone, but the spire is not so 
elevated, the base is more flattened, and the mouth is stated to be almost circular in that species, which besides 
has the whorls regularly convex from the simple sutures. 
Position and Locality —In the schists on the Bala limestone, Bryn-Melyn Quarry, near Bala, Merioneth- 
shire; Bala schists, Cymmerig, E. of Bala, Merionethshire. 
Explanation of Figure.—PI. 1. K. fig. 41, natural size, 
