PERICYCLUS ROTULIFORMIS. 



1 !'.» 



tion exactly corresponds with that of the ribs. Very fine transverse lines cover 

 the whole of the test, but they are too delicate to leave any impression upon the 

 cast. Beginning with the first whorl and extending to the penultimate one are a 

 series of small but conspicuous nodes or tubercles situated at the edge of the 

 umbilicus ; these apparently become obsolete on the last whorl. I have observed 

 them only upon a specimen from which the rock has been entirely removed from 

 the umbilical cavity (PI. XL, fig. 5). 



Dimensions. 







Type specimen in Museum 



of Science and Art, 



Dublin. 



Another specimen in 

 Museum of Science 

 and Art, Dublin. 



Diameter of shell . 



81 mm. 



73 



mm. 



,, umbilicus (edge to edge) . 



20 



30 



,, 



,, ,, (suture to suture) 



23 „ 



. about 25 



,, 



Height of outer whorl 



32-5 „ 



28 



,j 



„ above preceding whorl 



22 „ 



. about 22 



,, 



Thickness at umbilical margin 



32 „ 



33 



jj 



Affinities. — Its narrowly rounded periphery, shallower umbilicus, and strong 

 constrictions distinguish this species from Pericyclus Bailyi, Crick (p. 147), which 

 it superficially resembles. A rather coarsely ribbed, thick form, which may be the 

 young of P. Foordi, Crick, 1 is by these characters equally excluded from the 

 present species. 2 The deep constrictions in the latter cause it to be easily recog- 

 nised in all stages of growth ; these constrictions are somewhat deeper upon the 

 cast, but among numerous specimens collected only fragments of the test have been 

 preserved, so that this has not in any case presented a difficulty. 



Remarks. — Among the specimens of /'. rotuliformis submitted by the writer to 

 Mr. Crick, 3 he describes one which is somewhat more inflated than the type speci- 

 men from which his description was chiefly drawn up. In all other respects it 

 agrees with the latter. The dimensions of both are given above. 



The smaller of the specimens figured (PI. XL, fig. 5) belongs to the Wood- 

 wardian Museum, Cambridge, and was kindly lent to me by the museum authorities, 

 along with other specimens. 



Ijttniiitb'x. — St. Doulagh's, county of Dublin ; Grlenbane, county of Limerick. 



' This monograph (' Mem. Palaeont. Soc.,' vol. for L901), p. 1 M. 



'-' This monograph, p. 142. 



' • Aim. Mag. Nat. Hist.,' ser. 7. vol. iii, 1899, p. 136. 



