PERICYCLUS ROTULIFORMIS. 



149 



tioii 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 Avith the first whorl and extending to the penultimate one are a 

 scries of small l)ut conspicuous nodes or tubercles situated at the edge of the 

 umbilicus ; these apparently l)ecome obsolete on the last whorl. I have observed 

 them only upon a specimen from which the rock has l)een entire]}^ removed from 

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



Diameter of shell . 



,, umbilicus (edge to edge) 



„ ,, (suture 



Height of outer Avhorl 



„ above preceding whorl 



Thickness at umbilical margin 



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

 constrictions distinguish this species from rericijdus Baihji, Crick (p. 147), which 

 it superficially resembles. A rather coarsely ribl:)ed, thick form, which may l)e the 

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

 present species." The deep constrictions in the latter cause it to ])e 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. 



Remarl-fi. — Among the specimens of P. rotuUformis sul^mitted Ijy the wi'iter to 

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

 men from which his description was cliiefl}^ di-awn up. In all other respects it 

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



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

 wardian Musemn, Cambridge, and was kindly lent to me by th(< museum authorities, 

 along Avitli other specimens. 



Localities. — St. Doulagh's, county of Dublin ; Grlenban(>, cmuity of I limerick. 



I'or I'.iol), 



' This mono^rai>li (' Mciu. Palioont. Soc, 



- This incino-fiMph, p. 142. 



■^ ' Auii. Mag. Nat. Hist.,' ser. 7, vol. iii, 1899, p. 436 



in. 



