15« SILURIAN TRILOBITES. 



Localities. — Llandeilo Flags. Treiorwerth, near Llanerchymedd, Anglesea. 

 S. E. side of Arenig Mountain. Llangadoc, S. Wales. Caradoc or Bala Rocks, 

 everywhere in North Wales : Snowdon ; Bettws-y-coed ; Bala ; Dinas Mowddwy ; 

 Meifod ; Berwyn Mountains, &c. : fig. 5 is a fine specimen from near Waterloo Bridge 

 in the Vale of Conway ; and fig. 7 shows a specimen, distorted by cleavage, from Moel 

 Benddu, Dinas Mowddwy, (both in Mus. P. Geol.). Figs. 3, 4, and 6 are from Horderly 

 and the neighbourhood. It is extremely common in the Caradoc of Shropshire. 



Foreign Localities. — None. It is, like A. tyrannus, a truly British species. 



AsAPHUs (Basilicus) Marstoni, n. sp. PI. XXIII, fig. 1. 



A. parvus, vix uncialis, complanatus, ovato-ohlongus, oculis magnis capite cauddque 

 thorace brevioribus. Caput vix marginatum {angulis brevispinosis ?), oculis magnis remotis. 

 Glabella antice prominens, marginem fere attingens, haud lobata? Cauda ut in A. Powisii, 

 nisi brevior, subtrigona, axe angustiori costis distinctis, lateribus latimarginatis, costisque 

 utrinque 7 brevibus. 



This neat little species is evidently distinct from any other British form, nor do I 

 think it has been figured in European works. It might have passed as a young 

 A. Powisii, but for the great size of the eyes and the distinctness of the glabella ; for 

 the less relative size of the tail and the strength of its furrows would hardly be enough 

 to distinguish it, as these are the usual characters of young specimens. I think the 

 larger fragment belongs to it, but I shall describe the smaller one only. 



Half an inch long, and three tenths broad at the base of the head — the widest part ; 

 oblong-ovate, blunt in front and rather pointed behind ; the convex head as long as the 

 thorax, and each of them much longer than the tail. Glabella large, oblong, reaching 

 nearly to the front edge and almost overhanging it ; about one third the width of the 

 head. Cheeks strongly margined, bearing the large lunate eyes close to the glabella, 

 and much nearer the hinder margin of the head than in A. Potoisii ; the facial suture 

 beneath them not extending half-way out. Angles blunt ? (or with short spines). 



Thorax with a rather narrow axis, which tapers backwards, the rings somewhat 

 nodose. Fulcrum of the nearly direct pleurae placed beyond one third out, and strongly 

 grooved. The tail is half ovate, somewhat triangular in outline, with a narrow conical 

 axis reaching to the strongly concave margin, and sharply separated from the somewhat 

 depressed sides. The axis has six or seven distinct rings (nodose, like the hinder thorax- 

 rings) on the sides and middle, and the limb has about six abbreviated furrows, besides 

 the upper strong furrow which reaches, much beyond the others, nearly to the margin. 

 The concave margin has some concentric striae, which may be, and probably are, pressed 

 through the cast from the caudal fascia beneath. 



