GASTRIOCERAS CTRCUMXOIIOSUM. 197 



shell. ^\niorls rather nnmcroiis, their iiiiinl)er not precisely ascertainable; 

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

 one-third of the diameter of the shell in ^\•i(ltll, ^vitll steep sides, the edges snbangular 

 and tuberculated, only the edge of the inner whorls exjiosed. Whorl semilnnatc in 

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

 indented to neai'ly one-third of its height by the preceding whorl. Periphery very 

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

 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 curvatiu-e, 

 resemliling the lines ornamenting the test in Gaftfriorr'r((s Lisfcri, a well-known and 

 closely related species. The tul)ercles are somewhat lengthened in a direction at 

 right angles to the spiral of the shell, or, in other words, they radiate towni'ds the 

 centre of the uml)ilical cavity. 



Body-chamber and septa unknown. 



Dimensions. 



Plaster cast of the largest of the 

 original moulds. Firoda (Kil- 

 kenny). Dublin Mus. Sci. and 

 Art (Geol. Surv. Coll.). 



Diameter of shell . . . .31 mm. 



,, umbilicus . . . . 11 „ 



Height of outer whorl . . . . 1-5 „ 



,, above preceding whorl (about) . . 10 „ 



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



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

 compared. The most nearly related are Gasfrincrras TAstPvi [W. Martin], .). de ('. 

 Sowerby, sp. ; ' G. cnrhonariuni, von Buch, sp. ; and G. corondtnni, Foord and ("rick. 

 From the first of these G. circnnmoihisum is readily distinguished by its more con- 

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

 allied to this species. From G. rorhona rinm the present speci(>s differs in its nar- 

 rower and deeper umbilicus and its much more inflated form. (f. corannfnni. is an 

 allied form, but it has in all stages of growth more depressed whorls, a l)roader and 

 more flattened periphery, and a wider umbilicus than (t. rirciimnndnsuni. G. Jossae, 

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



' The numerous references to G. Listeri in the literature of Irish piilaeontology are erroneous. 

 Several specimens in the Griffith Collection (Dublin Mus. Sci. and Art) also are lal)elle<l " Goniatiten 

 Listeri ; " they are l)a<lly preserved specimens of rerirychie fasciruhitus, M'Coy. Tlie lalx'ls referred 

 to are prohaMy the ori<,'inal ones, dafinj^ from M'C<>y"s ' Synopsis ' (1844) ; the ink on them is nindi 

 faded. 



