118 TRILOBITES OF GIRVAN. 



Tail, short, semicircular, of two short segments fringed with from twelve to 

 fourteen long, radiating equal spines; a ridge from the anterior axis-segment is 

 continuous with the antepenultimate [?] spine on either side. General surface of 

 the head and body-rings slightly tubercular; surface of tail reticulated." (Wyville 

 Thomson.) 



Remarks. — A few more details may be added to the description of the head- 

 shield, the good specimens in Mrs. Gray's collection showing some additional 

 features; for Wyville Thomson had not very well preserved material for figuring, 

 and in none of his figures is the posterior part of the head-shield well shown. 

 Nicholson and Etheridge (oj>. cit.) also failed to represent it correctly, as an 

 examination of their type-specimens proves, and moreover they figured as belonging 

 to J. lalage two head-shields (op. cit., pi. viii, figs. 18, 19) which must be assigned 

 to other species ; only three of the specimens figured by them (op. cit., pi. viii, figs. 

 20 — 22) can be left in A. lalage, if we keep strictly to Wyville Thomson's definition. 

 The specimen figured by them in fig. 21 is in excellent preservation. In this head- 

 shield the anterior end of the median lobe of the glabella expands, so as to over- 

 hang the anterior pair of lateral lobes, and these lateral angles of the median lobe 

 are slightly nodular and notched behind so as to appear like a pair of small lateral 

 lobes (as in true homology they are) . The lobes of the so-called anterior or first 

 lateral pair are subcircular and completely circumscribed ; those of the second 

 pair are oval, longer, and also completely circumscribed. Behind them are narrow, 

 depressed, oblique occipital lobes, formed by the narrowed lateral portions of the 

 occipital ring; these pseudo-occipital lobes are marked off from the gibbous fixed 

 cheek by the continuation of the axial furrows, and from the broad median part of the 

 occipital ring by the continuation of the united furrows which mark off the lateral 

 lobes from the median lobe of the glabella. The shallow, broad occipital groove is 

 far forward, being nearly opposite the middle of the second pair of lateral lobes. 

 The median lobe of the glabella in front of it is broader than the lateral lobes, and 

 cylindrical in shape, but narrows slightly anteriorly. The occipital ring is so 

 enlarged as to be more than one third the length of the glabella, and it bears a 

 median tubercle as well as the pair of long divergent posterior spines. These 

 features are well shown (except the occipital lobes) in Wyville Thomson's figure 3, 

 pi. vi (pp. cit.). The axial furrows curve outwards and run obliquely backwards 

 in such a way as to give the glabella a hyperbolic rather than triangular shape. 

 The fixed cheeks are swollen to nearly the same extent as the glabella, and are 

 sharply marked off from it by the deep axial furrows ; a narrow, rounded, swollen 

 neck -segment is separated off by a deep neck furrow widening laterally. The eye- 

 ridge curves outward from the anterior end of the glabella to reach the eye, which 

 is small and situated opposite the middle of the second lateral lobes of the glabella, 

 ami distant less than half the width of the glabella at this level from the axial 

 furrow. The anterior margin of the middle shield is nearly straight, and is 



