ILL^ENUS OCULOSUS. 71 



The large associated epistoraes from Woodland Point and Rough Neuk which 

 probably belong to /. thomsoni measure relatively more from side to side than those 

 of 1. nexilis as figured by Salter (op. cit., pi. xxx, fig. 5), the proportions from side 

 to side and back to front being 1 : 2 instead of 2 : 3. The sides in these epistomes 

 also make a smaller angle with the front edge than in I. nexilis. The front border is 

 gently arched forwards, and the posterior border protrudes somewhat in the centre ; 

 the surface is crossed from side to side by 9 — 10 strong ridges. In a free cheek 

 from Rough Neuk the anterior submarginal continuation of the cheek to the 

 epistome is similarly ridged. This free cheek is of an elongated shape, rather more 

 than twice as long as wide, and pointed anteriorly at about 30°. The anterior and 

 posterior branches of the facial suture meet at the eye at about 135°. The genal 

 angle is widely rounded. 



The epistome from Penkill figured by Nicholson and Etheridge as /. nexilis ? 

 (op. cit, p. 158, pi. xi, fig. 12), and the head ascribed to I. murchisoni? from the 

 same locality (op. cit., p. 161, pi. xii, fig. 1), probably belong to this species. 



Collections. — Mrs. Gray (f. M.) ; Museum of Practical Geology; Edinburgh 

 Museum ; Woodwardian [Sedgwick] Museum. 



Horizons mot Localities. — Mullock Hill Group (L.Llandovery): Mulloch Hill ; 

 Rough Neuk. Saugh Hill Group (M. Llandovery) : Woodland Point. Camregan 

 Group (U. Llandovery) : Camregan ; Bargany Pond Burn. Penkill Group 

 (Tarannon) : Penkill. 



14 Illsenus cf. oculosus, Holm, 188G. Plate X, figs. 9—11. 



Description. — Head-shield convex, rounded, short, about one third wider than 

 long, strongly bent down in front and less so at the sides. Glabella wide, short, 

 with low median tubercle at base. Axial furrows curving inwards and converg- 

 ing anteriorly, but bending a little outwards near their front extremity, extend- 

 ing slightly in front of the eyes. Fixed cheeks about two thirds the width of the 

 glabella. Eye-lobes large, about one third the length of the head-shield, placed 

 close to the posterior margin, prominent, rounded. Facial sutures curving inwards 

 strongly from anterior margin to eyes, and behind them bending a little out to cut 

 posterior margin at about L5° just below eyes. Free cheeks broad, short, sub- 

 quadrate, as wide as long ; genal angle well rounded ; posterior margin nearly 

 straight; lateral margin strongly arched outwards. Eyes large, nearly half as Long 

 as free cheeks and one third the length of the head-shield, semi-annular, elevated 

 with prominent convex surface, less than half their length distant from posterior 

 margin; base of eyes surrounded by wide shallow groove. With' convex doublure 

 below free cheek (concave in cast). Narrow neck-ring present ? 



