DISCITOCERAS COSTELLATUM. 107 



DisciTOCERAS COSTELLATUM, F. M'Goij, sp. Plate XXVIII, figs. 4 a, b.' 



1844. Xautilus (Discites) costellatus, ^. Ji'Ci3_y. Synop. Carb. Foss. Ireland, 



p. 17, pi. li, fig. 4 (three figures). 

 1883. DisciTOCERAS COSTELLATUM, A. Hyatt. Genera of Fossil Cephalopods, 



in Proceed. Bo!<ton Soc. Nat. Hist., vol. 

 xxii, p. 292. 

 1891. DisciTES C0STELLATU9, A. H. Foord. Cat. Foss. Ceph. British Museum, 



pt. 2, p. 87. 

 1893. DisciTOCERAS COSTELLATUM, A. Htjatt. Carboniferous Cephalopods. 



Second Paper. Geological Survey of 

 Texas, Fourth Annual Eeport, 1892, 

 p. 435. 



Description. — Shell (fragment) discoid, consisting of portions of two of the 

 inner wliorls which are only in contact at the periphery ; tlie section is bi'oader 

 than high, about in the ratio of 9 : 11. Tlie umbiHcus is deep and of moderate 

 width. The periphery is broadly rounded, the sides are bhmtly angular, sloping 

 abruptly from the margin of the umbilicus to the point of contact of the preceding 

 whorl. The dorsal or anteperipheral area has a slight curvature corresponding 

 with the periphery of the whorl which it enfolds. The septa, as seen in a natural 

 section, are rather deeply concave; their distance apart is not known. The 

 siphuncle is central, or perhaps slightly above the centre in the young shell. The 

 body-chamber is not known. 



The ornamentation consists of about twenty-one fine longitudinal ridges, those 

 on the sides of the shell being both coarser and wider apart than those on the 

 periphery. The latter has a central ridge with three on either side of it closer 

 together than the width separating them from the central ridge; a slightly greater 

 space again occurring between the outer one of the three and the one of the coarser 

 series which, to the number of four, occupy the area extending to the edge of the 

 umbilicus. Within the latter only three can be seen in the specimen before me. 



Extremely fine, close-set lines of growth, barely visible to the naked eye, cover 

 the surface of the test, and show by their outline upon the periphery that the 

 aperture possessed a very deeply excavated hyponomic sinus. 



Affinities. — The character of its ornamentation would make this species easily 

 recognisable, and it also distinguishes it from other species of Discitoceras, of 

 which D. Wrightii is the nearest to it. The beaded ornamentation of the latter, 

 however, differentiates it readily from D. custellatum. 



RemarJiS. — The fragment now representing the present species in the " Griffith 



