10 F. R. Coicper Reed — Viidescrihed Trilohites. 



down the sides of the central portion from the lateral angles and 

 round the posterior margin, where it is broadest and slightly 

 excavated. The posterior angles are obtusely rounded. 



Measurements. 



mai. 



Length of hypostome ... 7*0 



Width of hypostome across middle ... ... 9-5 



Length of central portion 5-0 



"Width of central portion ... ... ... 7"0 



"Width of posterior border ... ... ... 2'0 



Rebiarks. — To none of the other British species of Liclias from 

 the Weniock Series does L. scutalis show any close resemblance. 

 L. verrucosus (Eichw.)/ with which it has been confounded, belongs- 

 to a lower stratigraphical horizon, and differs in the following 

 particulars, — the shape of the median lobe of the glabella, the 

 form and size of the basal lobes, the course of the axal furrows, 

 the position of the basal furrows, the course of the occipital furrow,, 

 the absence of a transverse groove across the median lobe of the 

 glabella, the position of the eye and eye -lobes, the shape of 

 the pygidium and the furrows on its lateral lobes, the shape of its 

 axis, etc., etc. In fact, Z. verrucosus is so utterly different from 

 L. scutalis that it is surprising that they were ever considered 

 identical or even closely allied. It is needless to enter into a minute 

 comparison of the two species, as their specific separation is obvious. 



Schmidt (loc. cit.) remarks that Z. scutalis is quite distinct from 

 Z. verrucosus (Eichw.). 



The species which shows most points of resemblance is Barrande's 

 L. ambiguus- from Etage Ee2, which is more or less equivalent 

 to our Weniock. This species has a glabella with anterior 

 lateral furrows continued down to the neck - furrow, with weak 

 middle and basal furrows, and with axal furrows having the 

 same general course and development as Z. scutalis, though less 

 curved inwards in the middle. The anterior lateral lobes are 

 closely similar, even to the indentation on the inner side, but they 

 are less oblique ; the middle lobes are rather less distinct, and the 

 basal lobes are only separable from them by their more swollen 

 character. There is also a somewhat similar shallow depression 

 across the neck of the median lobe. The smaller convexity of the 

 head-shield and the greater parallelism of the sides of the glabella are 

 points of difference. The occipital segment is also narrower, and the 

 occipital furrow has a different course. The thorax of Z. ambiginis 

 is unknown. It is in the pygidium that we find the most striking 

 points of resemblance : the shape of the axis and its continuation to 

 the posterior margin, the presence of only two pairs of pleuras on 

 the lateral lobes with their furrows, the projection of the extremities 

 of the second pair beyond the margin, the smooth unfurrowed 

 posterior portion of the lateral lobes, the flattened margin, the- 



1 Eichwald: Beitr. z. Iveuntn. RussL, Bd. viii (1843), p. 63, t. iii, fig. 23. 

 Schmidt: Rev. Ostbalt. Silur. Trilob., Abth. ii (1885), p. &2, t. ii, figs. 1-11. 



2 Barrande: Syst. Silur. Bohem., vol. i (1851), p. 60b, pi. xxviii, figs. 16-21. 



