GLYPHIOCERAH (BEYRICHOCERAS) SUBTRUNCATUM. 100 



faint lines of growth Avhicli on leaving the nmbilicns curve forwards, then a little 

 l)ackwards, and again more prominently forwai'ds so as to form a crest just below 

 the periphery. One or two shallow constrictions are seen upon th(> cast, Init the 

 test when present quite conceals them. 



Dimi'iisi<ni>i. 



Specinuui in llu^ Museum of 

 Science .aiul Art, Dublin 

 (Geological Survey Coll.). 

 Nantcnan. 



Diameter of shell . . . .70 mm. 



„ nmbilicns (edge to edge) . 7 ,, 



Height of outer whorl . . . . 39 „ 



,, above preceding whorl (about) . . 19 „ 



Thickness of shell at umbilical margin . . 30 ,, 



By comparing these measurements, taken from an undistorted specimen, with 

 those of Gh/jilnocerm^ {Beyricliocoras) irnncatum (p. 1()7), the greater thickness of 

 the shell in the present species becomes apparent. 



Affinitiox. — On comparing the figures of this species with those of (Uj/jthioccrds 

 (Bri/rirlinrcraf!) trnncdtnm, the chief resemblance between the tAvo will V)e clearly seen. 

 Both of them have the peripheral flattening more or less strongly emphasised in 

 the adult shell, and there is a similarity in the umbilical characters, smoothness of 

 the test, etc. ; but in the present species the shell is nmch thicker an<l more inflated, 

 and it is upon this character that the main distinction between the two species is 

 based. The peripheral lobe of the suture-line is also both broader and deeper in 

 G. (B.) ftnhinmcahim than it is in G. (7>.) tnnirafum., its greater breadth naturally 

 corresponding with the superior breadth of its peripheral area. G. (Z?.) virnnsfcDifi, 

 de Kon.,' is another species which will very well bear comparison with G. (//.) siiJifruii- 

 nifinu, and de Koninck points out its resemblance also to G. (/?.) trioicatum. It 

 differs from both in the greater size of its umbilicus in the adult stage of growth 

 and in the regular constrictions which occur in the young shell (De Koninck. 

 loc. cit., pi. xlviii, fig. 1). The larger size and angular margin of the nml)ilicus 

 in G. inconstant are the most striking differences between this species and G. 

 s)i]tfr>(ncatuni. 



The present species differs from G. ulifusvm in its more slender habit, in 

 the truncation or less broadly rounded character of the periphery, and in the 

 structure of the suture-line. 



lif'nuni-.t. — This species has so far been found chiefly in the .south and .south- 

 west of Ireland, in the counties of Tipperary and Limerick. 



1 Faune Calc. Carb. Belgiqup (Aun. Mus. I'oy. d'Hist. Nat. Bulyiquo, scr. Palcont., torn. v),pt. 2, 

 p. 120, pi. xlviii, figs. 4-9. 



