1G4 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



Description. — Shell subglobose, involute, slightly compressed on the sides which 

 are feebly convex and subparallel ; greatest thickness at the umbilical margin, 

 about four-sevenths of the diameter of the shell ; height of outer whorl about one- 

 half of the diameter of the shell. Inclusion of whorls almost complete ; umbilicus 

 very small and infundibuliform in the young shell, closed in the adult, with rounded 

 margin. Whorl semi-elliptical in section, height about five-sixths that of the width; 

 indented to about one-half its height l)y the preceding whorls. Periphery broadly 

 rounded, with a tendency to flattening in the adult shell near the extremity of the 

 body-chamber ; inner area very narrow. Body-chamber occupying at least an entire 

 whorl. Chambers not very deep, about fourteen in a whorl; suture-line as in 

 PI. XLII, figs. 7 '■, S c. Test nearly smooth, ornamented with very fine sinuous 

 lines of growth, which are strongly arched forward near the periphery, and form 

 on the latter a deep and broad sinus ; they arc sometimes accompanied by narrow, 

 obscure folds. One or two broad and shalloAv constrictions are generally present, 

 especially in adult shells. 



Dimensions. 



Diameter of shell 



,, uml)ilicus 



Height of outer whorl 



,, above preceding whorl 

 Thickness at uml)ilical margin 



Owing to distortion in both specimens these measurements are only approximate. 



Affiiiifics. — Mr. G. C. Crick and the author of this monograph have shown else- 

 where^ that Phillips had included two distinct species under the name " Goniatitcs 

 obtusus;" the original of Phillips's pi. xix, fig. 10, was selected as the type of 

 GlypMoccrns ohfnsnw, and the specimen represented by fig. 12 was separated from 

 the former under the name of Glypliioceras r]iiUi2>si. The differences which 

 distinguish the two species arc the following : — (J. {IJ.) riiillipsi has a more 

 compressed form and a more prominent umbilical margin than G. [11.) ohtiisum, 

 and thus it resembles G. (If.) diadema, Beyr., while its suture-line distinguishes it 

 from G. {B.) viicronofnm, to which it is also related. I have not recognised 

 G. rhilUpsi among the Irish fossils ; the type is in the " Gilbei'tson Collection " in 

 the British Museum (Register No. C. 5099 a), but the locality is unfortunately 

 unknown. G. (B.) ohtusum is distinguished from G. (Ji.) snhinincninm by its much 

 thicker shell, its rounded periphery, and its suture-line, and in the latter character 

 it differs materially from G. [B.) occidental e (p. 170). 



' Cat. Foss. Cepli. British Museum, pt. 3, p. IGO. 



