1-iO CARBONIFEROUS CEPHALOPODA OF IRELAND. 



moderately deep, witli subangular margin, about two-ninths the diameter of the 

 shell in width, partly exposing the inner whorls. Whorl semilunate in section, 

 considerably wider than high, indented to about one-third of its height by the 

 preceding whorl. Periphery broadly convex, merging into the rather flattened 

 sides ; inner (umbilical) margin rather steep, not very well defined. 



Body-chamber unknown. Suture-line as in PI. XXXVII, fig. 7 c. 



Shell (as indicated on the cast) ornamented with numerous rounded ribs, 

 numbering about five in the space of 1 cm., therefore more numerous than- in 

 P. fasciculatiis, in which there are only four in that space. Interspaces between the 

 ribs somewhat wider than the latter. The ribs bend backwards in passing over 

 the periphery, and form there a shallow median sinus. The fragments of the test 

 that remain are too imperfect to admit of the surface markings being determined. 

 So far as can be discovered in the somewhat unfavourable condition of the cast, 

 bifurcation of the ribs in the adult shell appears to be quite exceptional, but in the 

 young it occurs more frequently, though not as a characteristic feature, as in 

 P. fasciculatm. Constrictions separated by wide intervals are seen upon the cast, 

 which would probably be covered by the test when present. 



Dimensions. 



Specimen in Mr. Joseph 

 Wright's Collection. 



Diameter (longer) of shell (elliptical by rock pressure) 65 mm. 



„ „ umbilicus . . . 15 „ 



Height of outer whorl . . . . 32 „ 



„ ,, above preceding whorl . 21 „ 



Thickness at umbilical margin . . . J35 „ 



Affinities. — The resemblance between this species and P. fasciculatus has already 

 been adverted to ; the type of ornamentation is the same ; the points in which 

 they differ are sufficiently plain, and they are these : (1) the character of the 

 ribbing, which is much finer in the present species than in P. fasciculatus, bifurcation 

 being the exception in the former, and not the rule, as in the latter ; (2) the size 

 of the umbilicus, which is smaller in the present species than in P. fasciculatus. 



From P. Doohylensis the present species is distinguished chiefly by its coarser 

 ribbing ; it is thus seen that in this feature P. multicostatus comes between 

 F. fasciculatus and P. Doohylensis. 



The difference in the septation between P. multicostatus and P. Doohylensis 

 may be appreciated on comparing the figures of these species on PI. XXXVII 

 (figs. 7 and 8). 



BemarJcs. — The specimen from which the above description has been drawn up 

 was kindly lent to me by Mr. Joseph Wright. 



Locality. — Midleton, county of Cork ; Glenbane East, county of Limerick. 



