CARBONIFEROUS FOSSILS OF IRELAND. 3<j 



ractcr oi Plenrntomarla, but without tlic band, or the deep slit in the lip of that genus; the lines of frrowth 

 indicate a shallow, rounded sinus in the right lip, as in Janthina, but the great thickness of the shell in the 

 present species removes it very fur from such delicate shells, and, together with the form, might approximate it 

 to RuteUa ; but instead of the thick pad of enamel at the base of shells of that genus, the fossil is umbilicate. 

 Diameter six lines; height of spire three lines and a half 



Platyschisma zoNiTEs. MCoy. (PL V. fig. 17). 



Sp. CA.— Discoid; spire very depressed, obtuse, of five slightly convex whorls ; circumference rounded; 

 base flattened; umbilicus deep, rounded; surface nearly smooth, marked by obsolete lines of growth, havint' a 

 wide, backward bend in the middle of the whorls. 



This little shell so closely resembles a recent Zonites, as to have suggested the specific name ; it is more 

 depressed than any other species of Plati/schisma, although the number of whorls is greater than is usual in 

 that genus. Diameter seven lines and a half; height of spire tlu'ce lines. 



Pleukotomaria. De Fran. 



Gen. Ch. — Troclilform, generally Imperforate ; whorls frequently carinated ; a deep linear sinus in the 

 middle of the right lip. 



Pleukotomaria altavittata. M'Coy. (PI. V. fig. II). 



Sp. Ch. — Obtusely conical ; spire of three or four volutions ; whorls plane above, rounded below ; band pro- 

 minent, flattened, situated above the centre of the volutions ; sui-face smooth. 



This much resembles the P. ahdita, Phil., in shape, but is distinguished by the upper portion of the whorls 

 being tabulated, and the band, instead of being subsutural, as in that shell, is placed unusually high on the vo- 

 lutions ; the surface is quite smooth. Length six and a half lines, width eight lines. 



Pleurotomaria canalicuxata. M'Coy. (PL VI. fig. 3, a, b). 



Sp. Ch. — Shell conical, turreted, umbilicate ; upper third of the whorls flattened or concave at top ; a deep, 

 smooth channel runs along the angle which separates the upper flat portion from the descending portion of the 

 whorls ; spire acute, of five or six turns ; mouth nearly round ; all the whorls regularly and sharply striated spi- 

 rally. Height one Inch two lines, width one Inch three lines. 



This beautlfid shell Is very distinctly marked by the sulcus which runs along the upper edge of the whorls. 

 Height of spire one inch two lines, width at base one inch four lines. 



Pleurotomaria carinata. P/til. 



Helix carinata. Sow. Min. Con -Pleurotomaria carinata. Phil. Geol. York. 



Sp. Ch. — Obtusely conical, volutions gently convex; band broad, simple, smooth; oblique striae of the sur- 

 face very fine. Diameter one inch seven lines, height of the spire one inch one line. 



Pleurotomaria clathrata. M'Coy. (PL V. fig. 12). 



Sp. Ch. — Obliquely ovate ; spire acute, of four very convex whorls; mouth circular; mnbilicus very mi- 

 nute ; surface reticulated with sharp, prominent, transverse and concentric spiral ridges ; keel small, sharp, with 

 a broad, smooth groove on each side of it. 



This beautiful little shell is distinguished from the others of its genus by the great convexity of the whorls 

 of the spire, circular mouth, which, with the small umbilicus, regularly latticed surface, and smooth space above 

 and below the keel, renders the present one of the most distinctly marked and elegant of the genus. Length 

 two and a half lines, diameter of last whorl two lines. 



