104 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



Affinifles. — Discitoceras discors, F. M'Coy (a doubtful species), bears a close 

 resemblance to the present species, the ornamentation being exactly similar, the 

 difference between them consisting solely in the form of the whorls, which are 

 more or less rounded in D. Leveilleanum, subquadrate in D. discors. 



On comparing the present species with D. Wrightii, it is seen that the latter 

 has fewer whorls and a much smaller central vacuity, also that the ornamentation 

 is finer and of a different character, the finely beaded ridges in D. Wrightii 

 presenting a very different aspect from the ornament of D. Leveilleanum. 



Localities. — Clane and Naas, county of Kildare. 



? Discitoceras discobs, F. M'Goy, sp. Plate XXVII, figs. 4 a — e. 



1844. Natttiltjs (Discites) discobs, F. M'Coy. Synop. Carb. Toss. Ireland, 



p. 17, pi. iii, fig. 5. 

 1860. — DISCOBS, i2. Griffith. Journ. Geol. Soc. Dublin, vol. ix, p. 56. 



1878. — — L. G. de Koninch. Faune Calc. Carb. Belgique (Ann. 



Mus. Koy. d'Hist. Nat. Belgique, torn, ii), pt. 1, 

 p. 143, pi. XXX, figs. 8 a, b. 

 1883. DisciTOCEEAS DISCOBS, A. Hyatt. " Genera of Fossil Ceplialopods," 



Proc. Boston Soc. Nat. Hist., vol. xxii, p. 292. 

 1891. Discites discobs, A. R. Foord. Cat. Foss. Cepb. British Museum, pt. 2, 



p. 90. 

 1893. — — A. Hyatt. Carboniferous Cephalopods. Second paper. 



Geological Survey of Texas, Fourth Annual Report, 

 1892, p. 435. 



Description. — Shell discoid, compressed, consisting of about three, or at the 

 utmost three and a half volutions (not five, as stated by M'Coy), the sides of 

 which are exposed in a large and shallow umbilicus with a central vacuity of 

 moderate size. The section of the shell, in which lies its chief characteristic, is 

 subquadrate, the periphery slightly convex, nearly as broad as the sides, which 

 are flattened and distinctly angular at their edges, not rounded as in Discitoceras 

 Leveilleanmn. 



The size of the body-chamber is stated by de Koninck (loc. cit.) to be about 

 one-half of that of the last whorl. I have not seen it entire in any specimen. 



The siphuncle is said by de Koninck to be situated in the upper third of the 

 septa. 



The septa are moderately distant, varying from 6'5 to 8 mm. apart, at about 

 one-fourth of a whorl from the body-chamber, the last two being 5 mm. apart; 

 their sutures are sharply bent back at the sides and form an acute lobe, anteriorly 

 directed, upon the peripheral angles ; upon the periphery they forma shallow sinus. 



