Victorian Fossils, Part XVIII. 16B 



Cypkaspis lilydalemis, sp. dov. (Plate XIV, Fig. 6; Plate XVI., 



Pig. 19). 



Description. — Body suboval. Cephalon large in proportion to 



the rest, rapidly tapering to the pygidial extremity. 



Cephalon semi-circular, anterior border rounded and deeply 

 folded behind. Glabella of moderate size, inflated towards the 

 back; basal lobes pyriform, more deeply incised towards the lateral 

 glabellar sulci. Free cheeks missing. .Facial sutures deeply incised 

 in the middle, widely divergent to the anterior border, behind, 

 sweeping outwards to cut the posterior margin near the genal angles. 

 Glabella finely granulate. 



Thoracic segments 12; axis strongly inflated, slightly wider than 

 pleura ; axal furrows deeply incised. Pleura strongly convex 

 proximally, rapidly falling away from the fulcrum and becoming 

 concave at the outer margins; pleura medially furrowed, ends 

 bluntly rounded, or curving downwards to a blunt angle. 



Pygidium small : axis less than one-third of the width. 



Dimensions. — Total length of specimen (imperfect), 9 mm. 

 Approximate length when complete, 10.75 mm. Greatest width 

 of thorax. 6.5 mm. Greatest width of axis, 2.5 mm. Greatest 

 width of pleura. 2.25 mm. Length of cephalon, including neck- 

 ring, 3.6 mm. Length of glabella measured from neck-furrow, 2 

 mm. ; width, 2 mm. 



Relationships. — This trilobite belongs to the G. burmeisteri type 

 described by Barrande 1 , from the Ordovician and Silurian of 

 Bohemia. The axis in that species, however, is slenderer, and the 

 glabella longer, whilst the posterior extremity is not so tapering. 

 G. bowningensis, Mitchell, 2 somewhat resembles G . lilydalensis, dif- 

 fering in the longer and larger glabella, the narrower axis and the 

 broader posterior extremity. 



The British species, G. megalops, .McCoy sp., 3 is perhaps most closely 

 related to ('. lilydalensis, the chief points of difference in the latter 

 being the more oval outline of the body, absence of a thoracic spine 

 (although this may have become detached before fossilisation), and 

 the neater or smaller cranidial characters, as the glabella together 

 with the basal lobes. It may, therefore, be reasonably regarded as 

 a southern variant of the British form. 



1 S\sf. Sil. Boheme, vol. i., 1852, p. 484, pi. viii., figs. 61-71. . 



2 Pro<\ Linn. Soc. N.S. Wales, vol. ii., 2nd ser., pt. III. , 1S88, p. 418, pi. xvi., fig. 3. EHieridge 

 jnr. and Mitchell; ibid., vol. viii., 2nd ser., 1894, p. 170, pi. vi., figs. 3, 3<t-fi ; pi. vii., figs. 3 i-h, 



3 '.' Harpet mtpalops, McCoy, Syn. Sil. Foss. Ireland, 1846, pi. iv., fig. 5. 



Salter, Mem. Geol. Surv. Un. Kingd., dec. vii., 1853, pi. v. 12a 



