ILL.ENUS MEMORABI US. 165 



Illaenus extensus, Reed. 



1904. Illaenus extensus, Reed, supra, p. 61, pi. ix, figs. 3 — 5. 



In the type specimen of /. extensus the anterior margin of the head-shield was 

 broken and. imperfect, and its true proportions and shape could not be accurately 

 determined, but it appeared to be transversely semicircular. A small but complete 

 individual is now available from the same horizon and locality (Starfish Bed, 

 Thraive Glen) ; and though its surface is not so well preserved, the outline of the 

 head is well exhibited, and it is seen to be parabolic and not semicircular, being 

 somewhat pointed in front. The dimensions of this young individual, which, 

 though so small, possesses the typical nine thoracic segments and all the other 

 characteristic features of the species, are as follows : 



Length of head- shield . . . 5*00 mm. 



Width „ ... 10-50 „ 



Length of thorax .... 3 '00 ,, 



,, pygidium. . . . 3 - 75 ,, 



Width ... . . . 7'50 „ 



Illaenus macallumi, Salter. 



1904. Ilhenus macallumi, Reed, supra, p. 65. 



This species has now to be recorded from another locality in the Girvan district, 

 as in Mrs. Gray's new material there is a pygidium from Craigens (Mulloch Hill 

 Group, Lower Llandovery). 



Illaenus memorabilis, sp. now Plate XX, fig. \K 



1904 Illsenus cf. oculosus, Reed (pars), supra, p. 71, pi. x, fig. 11 (non figs. 9, lUj. 



Specific Characters. — The head-shield is only slightly convex from side to side 

 and from back to front, and is not bent down anteriorly. The middle shield is 

 subquadrate in form, the long anterior branches of the facial suture being sub- 

 parallel, and the width of the head between them only slightly greater than the 

 length. The eyes are rather large, and placed so far back as nearly to touch 

 the posterior margin; the eye-lobes are semicircular and project laterally, and the 

 surface of the cheek between them and the axial furrows is decidedly swollen. 

 The axial furrows present the most remarkable feature in the head-shield on 

 account of their length and course ; they converge at first rather strongly in their 



