150 CARBONIFET^OUS CEPHALOPODA OF IRELAND. 



Pkricyclus riJCATiLis, Tj. G. ih' Kuiiiiicl-, sp. Plate XLI, figs. 2 a — (/. 



1881. GoNiATiTEs PLicATii.iR, L. G. lie Konincli. Siir qiielqucs ci'plialopodes 



nouveaiix tlu calcaire carbouifore de 

 rirlande. Aun. Soc. gcol. de Bel- 

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

 pp. 50—60, pi. V, figs. 3, 4 (not 

 pi. vi, as erroneous!)' referred to). 



1899. Peeicyclus plicatilis, G. 0. Crick. Ann. Mag. Nat. Hist., ser. 7, vol. iii, 



p. 441. 



Dcsrrijjfion. — Shell siibglobose, ratlier 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 vcr}' 

 distinctly semilnnate in cross-section, much Avider than high ; indented to about 

 two-thirds of its height by the preceding whorl. Periphery l)roadly arched, imper- 

 fectly defined, merging into the slightly convex sides. Umliilical 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 ril)ljing it woidd appear to have had a broad 

 and moderately deep hyponoraic sinus. 



Suture-line as in PI. XLI, fig. 2 (/. 



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

 the sides of the shell, l)end somewhat abruptly l)ackwards 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. 



DiinciisioHs. 



Typo speoimon in Mu.soiim 



(if Science and Art, Dul)lin 



(Geoloffical Survey 



Collection). 



Diameter of shell (al)out) . . .85 mm. 



„ umbilicus (edge to edge) . . 38 ,, 



„ ,, (suture to suture) . . oO „ 



Height of outer whorl (about) . . . o4 „ 



,, above preceding whoi'l . . . 21 „ 



Thickness at umbilical margin (about) . . GO „ 



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



