AGNOSTUS BARRANDEI. L3 



The species with which this form is most likely to be confounded is A. barrandei. 

 The head of the latter is distinguished by the presence of axial furrows which 

 extend half the length of the head, while in A. alius only the basal lobes are 

 present and the glabella is otherwise entirely obsolete. In imperfect specimens, 

 however, this difference cannot always be discerned, as the axial furrows of 

 .1. barrandsi may be obscured. 



The axis of the tail in A. barrandei is surrounded by much stronger furrows 

 than in A. altus, while on the other hand, the segmentation of the axis is much 

 more distinct in A. altus, although even in this species it is not very strongly 

 marked. 



That this form belongs to Tullberg's section Leevigati can hardly be doubted ; 

 but it differs from most of the species of that group in having the pygidial axis 

 completely defined by the axial furrows. In this respect it agrees with Brogger's 

 A. Isevigatus v&r.forfex 1 and Matthew's A. laevigatas var. mamilla 2 and var. ciceroides. 3 

 From the two former it differs in the complete segmentation of the axis, and from 

 the last in its much greater size and in the fact that the second segment of the 

 axis is perfectly defined posteriorly. Our specimens agree completely with 

 Gronwall's A. alius except that, no doubt owing to compression, they are not so 

 convex in shape. All the British specimens that I have seen are distorted by 

 pressure. 



Horizon and. Localities. — Menevian : Porth-y-rhaw, St. David's ; Waterfall 

 Valley, near Maentwrog. 



9. Agnostus barrandei, Salter. Plate II, fig. 2. 



1872. Agnostus barrandei, Salter, Hicks, Quart. Journ. Geol. Soc, vol. xxviii, p. 176, pi. v, figs. 5, 6. 

 1902. Agnostus lens, Gronwall, Bornholms Paradoxideslag, p. 65, pi. i, figs. 8, 9. 

 1902. Agnostus lens, y&r.frontosa, Griiuwall, ibid., p. 66, pi. i, fig. 10. 



Head convex, rounded in outline, smooth or with minute tubercles, surrounded 

 by a narrow margin. Glabella marked off posteriorly by two longitudinal furrows 

 which extend for about half the total length of the head ; but anteriorly there is 

 no separation between the glabella and the cheeks ; basal lobes small. 



Thorax : axis formed of a central raised portion and two lateral tubercles ; 

 pleurae deeply grooved. 



Tail smooth or faintly tuberculate, rounded in outline, very convex, surrounded 

 by a narrow margin. Axis separated from the lateral lobes by deep axial furrows, 

 somewhat constricted at about a quarter of its length from the anterior margin, 



1 Brogger, Nyt Mag. for Naturv., vol. xxiv (1879), pi. v, fig. 6 a. 



2 G. F. Matthew, Trans. N. Y. Acad. Sci., vol. xv (1896), pi. xvii. fig. 2. 

 8 G. F. Matthew, ibid., pi. xvii, fig. 3. 



