152 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



are seen) shallow ; suture-line as in PI. XLI, fig. 1 c, but the apex of the lateral 

 lobe is not represented sufficiently acute. Test ornamented with coarse and rather 

 irregular ribbing or lines of growth, which, on leaving the umbilical margin, bend 

 backwards across the sides of the shell, and in passing over the periphery constitute 

 the broad and rather deep sinus already referred to. The lines or ribs here described 

 (they are somewhat obscure) are seen more distinctly upon the cast than upon the 

 test, only fragments of which are preserved. Some faint constrictions are seen 

 upon the cast of the body-chamber conforming in their direction to the lines of 

 growth. 



Dimensions. 



Type specimen in Museum 

 of Science and Art, 

 Dublin. 



Diameter of shell . . . .120 mm. 



„ umbilicus on the cast (edge to edge) . 33*5 ,, 



,, ,, „ (suture to suture) 31 ,, 



Height of outer whorl . . . 52 ,, 



,, above preceding whorl . . 33*5 „ 



Thickness at umbilical margin (about) . 44 ,, 



Affinities. — The comparative width of the shallow umbilicus and the compressed 

 form of the shell are features which bring this species into relationship with Peri- 

 cyclus Leesoni (p. 153), but the latter has a much narrower periphery, and is on the 

 whole a flatter and more slender shell than P. Clanensis. 



Remarks. — The present species is founded upon a single specimen contained in 

 the Museum of Science and Art, Dublin, and was originally labelled " Goniatites 

 Brownii" M'Coy, 1 but it bears very little resemblance to that species. 



Mr. Crick 2 referred the present species to Pericyclus, but its claim to belong 

 to that genus must be held to be somewhat doubtful, as the surface of the test is 

 badly preserved, and only fragments of it remain. The chief diagnostic character 

 of Pericyclus s is the presence of "strong, direct, transverse ribs." 



The late Professor Hyatt distinguished Pericyclus chiefly by its suture-line, in 

 which he recognised a spatulate external saddle, and an additional broad, angular, 

 lateral lobe, making two lateral lobes instead of one. This peculiarity is, I believe, 

 met with only in P. virgatus, de Kon. ; it is figured by Holzapfel. 4 The latter 

 species, along with P. princeps, de Kon., formed Mojsisovics' genus Pericyclus. 

 (J real variability is observable on comparing together the suture-line in different 

 species of Pericyclus, and it was upon this ground that Holzapfel urged that the 



1 ' Synops. Carb. Foss. Ireland,' 1844, p. 12, pi. iv, fig. 17. 



2 ' Aim. Mag. Nat. Hist.,' ser. 7, vol. iii, 1899, p. 436. 



3 ' Cat. Foss. Ceph. Brit, Mus.,' pt. 3, 1897, pp. 143, 144, figs. 68, 69 (respectively P. princeps 

 and P. virgatus — suture-lino). 



* 'Palseont. Abhandl.,' Dames und Kayser, vol. v, I, p. 34, pi. iii. 



