GLYPHIOCERAS (BEYRICHOCERAS) DIADEMA. J 81 



simple and their course is nearly straight. A number of shallow constrictions (from 

 three to five per whorl) concurrent with the striae are present, and are more 

 conspicuous on casts. Initial chamber ellipsoidal or spindle-shaped, transversely 

 elongate." 



" This species is very variable : sometimes it has a relatively small umbilicus 

 and a rather finely ornamented test, the young having much the same characters 

 but being rather more inflated; sometimes it has an open umbilicus and a more or 

 less coarsely striated test, the ornaments being much coarser in the young than in 

 the adult. Since there are intermediate forms connecting the two extremes, and as 

 they all have the same form of suture-line, we refer them to one species. 



" Shell attaining a diameter of GO mm." ( ' Cat. Foss. Ceph.,' loc. cit.) 



Affinities. — This species is not unlike the young forms of Glyphioceras {Beyrich- 

 oceras) truncatwm, but the periphery is rounded, and, when the suture-lines are 

 compared, it is seen that the resemblance is only superficial and external. A feature 

 which calls for notice in the suture-line of the present species is the considerable 

 height and width of the peripheral lobe, for which it is difficult to find a parallel in 

 any other species of Glyphioceras, the only one coming near to it being G. Phillipsi, 

 Foord and Crick. 1 This species differs, however, from the present one in its more 

 compressed form and narrower umbilicus. As compared with G. (B.) excavatum, 

 J. Phillips, G. (B.) diadema has a smaller umbilicus and very distinct sigmoidal 

 lines of growth, while the suture-line has a much more elevated median saddle. 



Remark*. — I have referred some specimens rather doubtfully to this species. 

 These are represented by figs. 4, 5, and G on PI. XL VII, and fig. 8 on PI. XLIX. 

 The former consist of pyritised casts contained in a slaty rock, from which it is 

 difficult to extract them whole. The suture-lines are beautifully preserved, and 

 appear as delicate lines traced upon the smooth surface of the cast. The specimens 

 are all small, the largest measuring only 27 mm. in diameter, the smallest about 

 12 mm. Shallow constrictions are present in all the specimens. 



A specimen in the museum of the Royal College of Science for Ireland, from a 

 locality " four miles east of Loughrea," seems also to have some claim to belong to 

 the present species. The lines of growth have the distinctly sigmoid curvature in 

 crossing the sides of the shell, characteristic of G. (//.) diadema. The periphery is 

 somewhat depressed, and the umbilicus is small. The sutures are not seen. The 

 specimen measures 48 mm. in diameter. 



The specimen figured on PI. XLIX (fig. 8) has now to be referred to. The most 

 prominent feature in this is the distinctly sigmoidal character of the lines crossing 

 the sides of the shell, and becoming more prominent where they bend sharply 

 forward near the periphery. This is quite characteristic of the species to which 



1 'Cat. Foss. Cepk. British Museum,' pt. 3, p. 172, t'iL?. 80 (suture-line). 



