Crusracea. | LOWER PALAXOZOIC ARTICULATA. 147 
TRETASPIS SETICORNIS (fis. Sp.) 
Syn. and Ref.—Asaphus seticornis. Hisinger Leth. Suec. Pl. 37. fig. 2. 
Sp. Ch.—Cephalie shield closely granulated, nearly semicircular, about twice as wide as long; angles 
prolonged into slender spines directly backwards; margin broad, four rows of punctures in front, more 
numerous at the sides, usually a smooth furrow separates the outer two rows of punctures from the rest ; 
glabella having the anterior half nearly spherical, posterior half abruptly contracted to a narrow neck, with 
a distinct neck-furrow and two short segmental furrows at each side, the ends forming three deep punctures 
in casts; cheeks spherical triangles, convex, as high as wide, traversed diagonally by the eye-line and 
having a small ocular tubercle in the middle; pygidium obtusely rounded, more than twice as wide as 
long, seven segments in the axal lobe, six on the lateral lobes. Length of head about five lines. 
Position and Locality—tIn the slates of Moel y Gunnedd uchat, W. of Bala Lake, Merionethshire ; 
Alt yr Anker, Meifod, Montgomeryshire; Cwm of the Cymmerig, Bala. 
Genus. AMPYX (Dal.) 
Gen. Char—Buckler trigonal; glabella very large and prominent, narrow behind, and having a long 
slender process projecting upwards and forwards from its anterior end; cheeks flattened, posterior lateral 
angles prolonged backwards into long slender spines; (? no eyes nor eye-lines) ; thoraw of five or six flattened 
segments, the sides straight, divided by a large diagonal pleural groove, which is narrow and close to the 
upper edge near the axis, gradually widening towards the obtuse ends; pygidiwm nearly as large as the 
buckler, subtrigonal, one strong anterior segmental furrow ; axis faintly marked with numerous transverse 
furrows, sides smooth or ribbed, flat, with a narrow vertical margin. 
From the examination of a vast number of specimens in various states of preservation, I think I have 
ascertained the course of the facial sutures in the A. nasutus (Dal.) and A. nudus (Murch. Sp.); they run 
almost parallel with the furrows which separate the glabella from the cheeks on each side, from the front 
nearly to the posterior margin, near which they turn outward and finally cut it at a short distance from 
the base of the glabella; there is a tumid spot about the middle of the eye-line which may be an eye, 
the proximity to the sides of the glabella rendering it difficult to detect 
Ampyx LATus (M°Coy). Pl. 1. E. fig. 13. 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Sp. Ch.—KEntire animal transversely oval, length one-fifth less than the width; cephalic shield smooth, 
front margin regularly curved, width three-fifths the length; g/abella moderately tumid, pyriform, having 
a narrow vertically elongate (? ocular) swelling close to the middle third of each side, and two short, minute, 
segmental furrows at each side of the narrow base; thoracic segments five, pleuripedes of each side twice 
the width of the axal lobe; pygidiwm very obtusely and regularly rounded, four times wider than long, 
axis with about seventeen minute segmental furrows, sides with about eight. Length of entire animal 
three and a half lines. 
This rare species is most allied to the A. parvulus (Forb.) and the A. nasutus (Dal.), from both which 
the perfect animal is easily known by its transversely oval form; the regular curvature, and great width 
of the cephalic shield, and of the pygidium, easily distinguish these parts when found separate; the latter 
agreeing nearly in form with that of the A. parvulus, from which it differs equally with the other in all 
the other characters of cephalic shield, &c. 
Position and Locality—Rare in the Black shale, three miles N. of Builth, Radnorshire. 
Explanation of Figures—P\. 1. E. fig. 13. Natural size, black shale, three miles N. of Builth—Fig. 
13a. Ditto, magnified three diameters. 
u 2 
