ILLt^NUS LATUS. 23 



With the exception of the following trifling differences, probably of n o tjpecific 

 value, the "glabellas" of the present specimens agree completely with those 

 previously described by me ; (1) the double row of small tubercles bordering the 

 median groove on the first segment is not so distinct, and the tubercles are more 

 irregularly disposed, increasing progressively in size backwards to the first furrow, 

 so that there is a cluster of three to four large tubercles on each side of the posterior 

 end of the groove ; (2) the third pair of furrows do not have such marked hooked 

 inner ends as in most Whitehouse examples, but the parts of these furrows which 

 are arched forwards have a short horizontal furrow behind, separating off from the 

 segment a small transverse area on each side, just as Barrande shows in one 

 figured specimen (o/). cif., fig. 30). However, these differences between our 

 previously figured specimens and the present one are trifling and immaterial, and 

 they must be referred to the same species. 



From Barrande's B. stupeiida our form differs in the shape of the fourth and fifth 

 segments, in the presence of strong tubercles down the middle of the first segment, 

 in the presence of a narroAV occipital ring and in the triangular projection of the 

 border in front. If we regard the lateral band on each side of the first segment 

 as the anterior part of the fixed cheek or eye-lobe, then it will be defined outside 

 by the facial sutures, and they cross the anterior border obliquely, meeting at an 

 acute angle in the median line so as to leave a triangular piece of the border 

 between them. 



This Whitehouse form may now receive a specific name and be known hence- 

 forth as B. scotica. 



As regards the zoological position of the curious genus BolienvUla, it may be 

 suggested that it is not a trilobite at all, but is referable to some primitive section 

 of the Arachnida. 



Genus ILLJENUS, Dalman. 

 lUaenus latus, M'Coy. 



1904. Illxnus latus, M'Coy, Eeed, op. cit., pt. ii, p. 63, pi. ix, figs. 6, 7. 



The occurrence of this species in the Balclatchie Group is now established, 

 some typical pygidia having been recently found by Mrs. Gray, at Balclatchie. 

 The characters by which the pygidium is distinguishable from that of J. portlocJci 

 have been previously given, but it is doubtful if we can satisfactorily separate the 

 head-shields, as they both occur in the same bed and a complete individual is 

 unknown, isolated and non-associated head-shields and pygidia of the two species 

 being only found. On the strength, however, of the pygidial axis in /. latus being 

 narrower^than that in I. portlocM, it is probable that the head-shields with the 

 narrower glabella are referable to I. latus. 



