BRITISH FOSSILS. 



Decade II. Plate VII. 



OGYGIA POETLOCKIL 



[Genus OGYGIA. Brongniart. (Sub-kingdom Articulata. Class Crustacea. Order 

 Entomostraca. Family Trilobitaj). Eyes large, smooth; facial suture cutting the pos- 

 terior margin ; no rostral shield or vertical suture ; hypostome entire ; body rings 8 ; tail 

 large.] 



Diagnosis. O. ovali-oblonga ; capitis margine angusto; glahelld geiiis 

 latiore^ obscure lobatd ; oculis ad aiiteriorem partem capitis positis ; sutura 

 faciali ad fr07item marginali ; caiid<B axi lato brevissimo. 



Synonyms. Asaphus dilatatus, Portlock (1832), Geol. Rep., Tyrone, 

 &c., pi. 24, f. 2 (not of Dalman). Ogijgia dilatata, Phillips, Memoirs 

 Geol. Survey (June, 1848), vol. ii., pt. 1, 239. 



Description. — Length 3^ inches ; width 2^ inches ; often larger. 

 General form nearly flat, ovate, widest in front. Head forming rather 

 more than a semicircle, considerably longer and wider than the tail, 

 but about as long as the thorax ; the glabella is as wide as the cheeks 

 below, and separated by slight furrows from them ; it widens and over- 

 hangs the eyes above, and is abruptly bent down in front, where the 

 margin is hardly visible. For nearly two-thirds of its length the gla- 

 bella is marked by lateral furrows, irregular in direction, dividing it 

 (apparently) into four lobes, exclusive of the forehead and neck lobes. 

 The neck lobe b is broad, and rises higher on each side than in the 

 middle ; it has two oblique sunk lines, c c, rising from the lower angles, 

 which appear to divide it into a pair of lobes ( O. Buchii has the same 

 marking). Above this lobe lies the more contracted basal one ^, 

 which does not reach to the margin of the glabella. The second lobe, Zt, 

 is wider and more oblique than the third, z, which is very faintly divided 

 from the wide transverse forehead lobe a. The fourth lateral lobe, so 

 distinctly marked in O. Buchii, is absent in this species. Eyes mode- 

 rate, placed very high up, towards the termination of the facial suture 

 on the margin ; eye -lid semi-lunate, but not constricted above or below ; 

 eye line turning a little out above the eye, beneath it obliquely down- 

 wards and outwards, cutting the posterior margin at about half the 

 cheek's width ; wings moderately large, with a narrow border and a 

 [ii. vii.] 2 G 



