14 BRITISH CAMBRIAN TRILOBITES. 



again widening out and finally terminating in a blunt point some distance in front 

 of the margin ; divided into three segments, but the dividing furrows are faint and 

 frequently obsolete ; there is a median tubercle on the middle segment. When 

 visible, the anterior segment is very short ; the middle segment narrow, hexagonal 

 in shape, bearing a median tubercle at its posterior extremity; the posterior 

 segment forms more than half the total length of the axis. 



Head- and tail-shields up to 7 or 8 mm. long and wide. 



Agnostus barrandei is distinguished from A. alius by the presence of axial 

 furrows defining the glabella for about half the length of the head, by the much 

 deeper axial furrows of the tail, and by the very vague and indistinct nature of the 

 segmentation of the tail axis, which is indeed generally obsolete. 



Types. — The originals of Hicks's figs. 5 and G are in the Sedgwick Museum, 

 Cambridge. 



Horizon and Localities. — Menevian : Rhaiadr ddu, near Maentwrog ; Cwm 

 hesian, Mawddach ; Tyddyngwladys ; Porth-y-rhaw and Penpleidiau, near 

 St. David's. 



10. Agnostus rotundus, Gronwall. Plate II, figs, o, 4. 



1902. Agnostus rotundus, Gronwall, Bornholms Paradoxideslag, p. 78, pi. i, fig. 19. 



Head slightly convex, rounded in outline, with a rather narrow margin. The 

 basal lobes are defined, but there is no other trace of the glabella. 



Thorax : axis with a wide central portion and a small lateral nodule on each 

 side, which is distinctly separated from the rest of the axis by a furrow which 

 runs obliquely forward and inward. The pleura? of the first segment are grooved 

 by a furrow near the posterior margin. 



Tail rounded in outline, not very convex. Axis rather wider than the lateral 

 lobes, not segmented, widest near the front, with a small median tubercle at end of 

 anterior third, decreasing rapidly and regularly backwards till it terminates in a 

 blunt point. Lateral lobes widest in front, narrow slightly posteriorly, and con- 

 fluent behind the axis, where they are narrowest. Axial and marginal furrows 

 dee}) ; the axis and lateral lobes are not in themselves gibbous, so that if the 

 furrows were filled up the whole tail would be uniformly convex. 



Head- and tail-shields about 3*5 — 4 mm. long and wide. 



In some collections tins species has been called A. scutalis, Salter, although it is 

 not one of the various forms included by Salter under that name. It is easily 

 distinguished from A. exaratus by the absence of the groove behind the axis of the 

 tail, and by tlie much shallower axial furrows. The axis, moreover, is not con- 

 stricted and the lateral lobes narrow posteriorly, while in J. exaratus they expand. 



