GASTEIOCERAS OIRCUMNODOSUM. 197 



shell. Whorls rather numerous, their number not precisely ascertainable; 

 probably six or seven. Inclusion nearly complete. Umbilicus rather more than 

 one-third of the diameter of the shell in width, with steep sides, the edges subangular 

 and tuberculated, only the edge of the inner whorls exposed. Whorl semilunate in 

 section, considerably wider than high, but the exact proportions cannot be given ; 

 indented to nearly one-third of its height by the preceding whorl. Periphery very 

 broadly arched, merging in the lateral area. Umbilical walls steep, with subangular 

 margin, bearing a single row of tubercles, which give rise to fine lines crossing the 

 periphery, the nature of which cannot be very distinctly made out owing to the 

 weathering of the fossil, but they appear to be fairly regular, raised lines, probably 

 varying in prominence, crossing the periphery, with a very slight curvature, 

 resembling the lines ornamenting the test in Gastrioceras Listeri, a well-known and 

 closely related species. The tubercles are somewhat lengthened in a direction at 

 right angles to the spiral of the shell, or, in other words, they radiate towards the 

 centre of the umbilical cavity. 



Body-chamber and septa unknown. 



Di 



mensions. 



Plaster cast of the largest of the 

 original moulds. Firoda (Kil- 

 kenny). Dublin Mus. Sri. and 

 Art (Geol. Surv. Coll.). 



Diameter of shell . . . .31 mm. 



,, umbilicus . . . .11., 



Height of outer whorl . . . . 15 ,, 



above preceding whorl (about) . . 10 „ 



Thickness- at umbilical margin (about) . . 20 ,, 



Affinities. — There are several species with which the present one may be 

 compared. The most nearly related are Gastrioceras TAsteri [W. Martin], .1. de C. 

 Sowerby, sp. ; 1 G. carbonarium, von Buch, sp. ; and G. coronatum, Foord and Crick, 

 from the first of these G. circwn/nodosum is readily distinguished by its more con- 

 tracted umbilicus and proportionately narrower periphery ; it is certainly very closely 

 allied to this species. From G. carbonarium the present species differs in its nar- 

 rower and deeper umbihcus and its much more inflated form. G. coronatum is an 

 allied form, but it- has in all stages of growth more depressed whorls, a broader and 

 more flattened periphery, and a wider umbilicus than G. circumnodosum. G. Jossse, 

 de Verm, though resembling the present species in its encircling tubercles, has 



1 The numerous references to CI. Llxfn-i in the literature of Irish palaeontology are erroneous. 

 Several specimens in the Griffith Collection (Dublin Mus. Sci. and Art) also are labelled " Goniatites 

 Listeri;" they are badly preserved specimens of Pericyclus fasciculatus, M'Coy. The labels referred 

 to are probably the original ones, dating from M'Coy's ' Synopsis ' (1844) ; the ink on them is much 

 faded. 



