144 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



related species to P. subplicatiUs. I have found, in fact, no inconsiderable 

 difficulty in distinguishing the two, in spite of Mr. Crick's careful diagnosis of 

 them ; this difficulty arises partly from the imperfection of the specimens available 

 for description when he wrote, and partly from the fact that there are no 

 specimens of the young shell of P. subplicatiUs to compare with that of P. Foonh, 

 which shows it exposed by the breaking away of the outer whorl. There is good 

 reason for supposing, however, that the young shell in P. subplicatiUs was much 

 more compressed in form than that of P. Foordi, which is remarkable at this stage 

 of growth for the breadth of its whorls compared with their height — a feature 

 which is not maintained in the adult shell. On a comparison of the ornamentation 

 of the two species it is seen that in P. Foordi the ribbing when crossing the 

 periphery makes a broader median sinus than that of P. subpUcatilis, and this is 

 found to be due to the considerably greater l^readth of the periphery in the former 

 species, perhaps the most easily distinguishable feature when an appeal has to be 

 made solely to external characters. 



When the sutures are compared it will be observed that there are not wanting 

 distinctive marks whereby the differences between the two species are further 

 accentuated. These consist (1) in the greater proximity of the sutures, indicating 

 shallower chambers in P. Foordi ; (2) in the disposition of the lateral in relation to 

 the peripheral lobe in that species when contrasted with P. subplicatiUs. 



Bemarhs. — This species is rather plentiful at St. Doulagh's, though the 

 specimens hitherto collected there are all more or less imperfectly preserved, and 

 some are in a crushed condition. 



I must express my great indebtedness to the authorities of the Woodwardian 

 Museum, Cambridge, represented by Mr. F. R. Cowper Reid, M.A., F.G-.S., who 

 most kindly sent me several interesting specimens obtained at St. Doulagh's, one 

 of which is figured on PL XXXVIII. By the loan of these specimens I have been 

 much assisted in completing the description of the present species. 



Locality. — St. Doulagh's, county of Dublin. 



Pericyclus trapezotdaijs, G. C. Crick. Plate XXXIX, figs. 2 a — d. 



1899. Pericyclus trapezoidalis, G. C. Crick. Ann. Mag. Nat. Hist., ser. 7, 



vol. iii, p. 432, fig. 2. 



Description. — The original diagnosis runs as follows : — " Discoidal, flattened, 

 rather widely umbilicated ; greatest thickness at the margin of the umbilicus, 

 nearly four-elevenths of the diameter of the shell ; height of outer whorl about 

 four-elevenths of the diameter of the shell. Whorls fairly numerous (exact number 

 not known) ; inclusion rather more than one-half ; umbilicus shallow, displaying 



