U2 CARBONIFEEOUS CEPHALOPODA OF IRELAND. 



suture-line lias been artificially worked out in a young shell, with a diameter of 

 68 mm., from Cloghran,^ in which it is very clearly shown (PI. XXXVIII, fig. 4). 

 (2) Another feature worthy of note is a flattening of the peripheral area in the young 

 shell, scarcely observable in the (older) type specimen. This flattening amounts 

 almost to truncation at this stage of growth, but becomes obsolete at a diameter of 

 about 100 mm. In the young shell above referred to it defines the area of the peri- 

 phery, upon which the ribs are disposed in a remarkably regular manner, as observed 

 by Mr. Crick. (3) Judging by the new material placed at my disposal, I think 

 Mr. Crick's estimate of the number of whorls in this species is somewhat excessive. 

 The original specimen, of which I have a plaster cast before me, is broken across 

 the umbilicus, making it difficult to compute the number of the younger whorls. 

 I should put down the total number of whorls at about five, or six at the utmost. 



Affinities. — The subject of the relationship of the present species to Pericyclus 

 suhj)Ucatilis, Crick, is discussed under the description of the latter (below) ; it will, 

 therefore, only be necessary here to refer to some other species which it resembles. 

 P. rotuliformis, Crick,^ may be taken first; this species bears at least a general 

 resemblance to P. Foorcli in form and ornamentation, but as respects the first it is 

 a flatter shell, and as to the second feature the ribbing is stronger, and it 

 possesses, in addition, very strong periodic constrictions which give it the wheel- 

 like aspect that suggested its name. In P. Baihji, Crick,^ we have a species 

 which, while it has a decided resemblance to the present one in its ornamentation, 

 differs from it in its much more inflated form and relatively larger umbilicus. 



Localities. — St. Doulagh's (type specimen) and Cloghran, county of Dublin. 



Pericyclus subplicatilis, G. C. Grid: Plate XXXVIII, figs. 1 (/, h, 2. 



1899. Pericyclus subplicatilis, G. C. CricJc. Ann. aiid Mag. Nat. Hist., ser. 7, 



vol. iii, p. 442, figs. 8, 9. 



Description. — Mr. Crick gives the following description of this species : — " Shell 

 discoidal, somewhat compressed, moderately widely umbilicated ; greatest thick- 

 ness almost close to the margin of the umbilicus, about two-fifths of the diameter 

 of the shell ; height of outer whorl about two-fifths of the diameter of the shell. 

 Whorls six or seven, inclusion four-fifths ; umbilicus rather deep, with subangular 

 margin, exposing the edges of the inner whorls, about three-tenths of the diameter 

 of the shell in width. Whorl semi-elliptical in cross-section, about as high as 

 wide, indented to about one-fifth of its height by the preceding whorl ; periphery 



1 Now in the British Museum (No. C. 7973). 



2 'Ann. Mag. Nat. Hist.,' ser. 7, vol. iii, 1899, p. 434, fig. 3. 



3 Ibid., p. 438, figs. 6, 7. 



