150 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



Peeicyclus plicatilis, L. 0. de Koninch, sp. Plate XLI, figs. 2 a — d. 



1881. Goniatites tlicatilis, L. G. de Koninch. Sur quelques ceplialopodes 



nouveaux du calcaire carbonifere de 

 l'lrlande. Ann. Soc. gcol. de Bel- 

 gique, torn, ix, 1881-82 (Memoires), 

 pp. 50—60, pi. v, figs. 3, 4 (not 

 pi. vi, as erroneously referred to). 



1899. Pericycltts plicatilis, G. C. CricJc. Ann. Mag. Nat. Hist., ser. 7, vol. iii, 



p. 441. 



Description. — Shell subglobose, rather widely umbilicated ; greatest thickness at 

 the umbilical margin, about two-thirds of the diameter of the shell ; height of outer 

 whorl about two-fifths of the diameter of the shell. Number of whorls not ascer- 

 tainable ; inclusion almost complete ; umbilicus deep, about one-third of the diameter 

 of the shell in width, exposing the angular edges of the inner whorls. Whorl very 

 distinctly semilunate in cross-section, much wider than high ; indented to about 

 two-thirds of its height by the preceding whorl. Periphery broadly arched, imper- 

 fectly defined, merging into the slightly convex sides. Umbilical zone well defined, 

 rather wide, nearly perpendicular to the plane of symmetry of the shell with a little 

 inclination towards the centre of the umbilicus. 



Body-chamber occupying at least the whole of the last whorl. Aperture not 

 preserved, but from the direction of the ribbing it would appear to have had a broad 

 and moderately deep hyponomic sinus. 



Suture-line as in PI. XLI, fig. 2 d. 



Test ornamented with slender but prominent ribs, which, arching forwards upon 

 the sides of the shell, bend somewhat abruptly backwards and form upon the 

 periphery a broad and moderately deep hyponomic sinus ; the interspaces are 

 somewhat wider than the ribs ; the whole surface of the test is covered with fine 

 lines of growth. 



Dimensions. 



Typo specimen in Mnsenm 



of Science and Art, Dublin 



(Geological Survey 



Collection). 



Diameter of shell (about) . . .85 mm. 



„ umbilicus (edge to edge) . . 38 ,, 



,, ,, (suture to suture) . . 30 ,, 



Height of outer whorl (about) . . .34 ,, 



,, above preceding whorl . . 21 ,, 



Thickness at umbilical margin (about) . . 00 „ 



Remark*. — De Koninck's measurements of this species are: — Longitudinal 



