Yol. 65.] ROCKS OF THE TOTTEMAKEADY DISTRICT. 143 



immediately in front of the glabella); posterior margin' not straight, 

 bnt bending back on each side of the glabella. Glabella very- 

 broad and short, about one-third the length of the head-shield, 

 with a slight independent convexity near the base ; axial furrows 

 deep, subparallel, rather sigmoidal, curving gently at first outwards, 

 then inwards, and then outwards again, ending behind the front of 

 the eyes. Fixed cheeks narrow, about a third of the width of the 

 glabella, with very weak convexity at the base, and the posterior 

 margin making an angle with the base of the glabella. Eye-lobes 

 large, semicircular, situated far back at about one-half to two-thirds 

 of their own length from the posterior margin of the head, and distant 

 from the axial furrows about one-third of the width of the glabella. 

 Facial sutures in front of the eyes subparallel and nearly straight, 

 but curving in convergently very close to the anterior margin ; 

 facial sutures behind the eyes very short, bending outwards, slightly 

 divergent, cutting the posterior margin at about 45°-60° immediately 

 behind the eyes at about one-third the width of the glabella from 

 the axial furrows. Free cheeks broad, rounded, nearly as wide 

 as long, about two-thirds the width of the glabella, with a broad, 

 regularly rounded genal angle, the posterior and lateral margins of 

 the free cheeks forming one continuous semicircular curve. Eyes 

 large, prominent, more than one-fourth of the length of the head- 

 shield, semicircular, with a large convex lens-bearing surface steeply 

 inclined and constricted at the base, with a surrounding Avide 

 shallow furrow. Test minutely and closely punctate, and anterior 

 part of head-shield ornamented with a few subconcentric terrace- 

 lines starting from about the middle of the lateral margin of the 

 free cheeks and crossing over the middle shield. 



Length of head on curve 100 millimetres. 



Width of head on curve 15'5 „ 



Width of glabella 5-0 



Width of fixed cheek at base 1'75 ,, 



Length of eye 2 - 75 „ 



Remarks. — This species is by far the most abundant repre- 

 sentative of lllcenus in the limestone exposed at (58) west of 

 Gortbunacullin Farm. There are associated with the head-shields 

 some imperfect pygidia, which probably belong to the same species, 

 but their characters are not completely known (PI. YI, fig. 2). 

 They have a transversely semicircular shape, with the fulcrum far 

 out, at about one-eighth the total width of the pygidium, and the 

 truncated anterior lateral angles oblique and small, being cut off 

 at about 45°- 60° to the anterior margin, which is straight. The 

 axis is prominent, projects on the margin, and has a decided 

 independent convexity : it is triangular in shape, measuring about 

 a third to a half of the length and about a third of the width of 

 the pygidium. It is feebly defined near the apex, and when the shell 

 is removed a median groove is seen to run from it to the posterior 

 margin across the fascia. The caudal fascia is very wide behind, 

 being nearly half the length of the pygidium, but at the sides it 



