170 BRITISH PALAZOZOIC FOSSILS. (Crustacea. 
Isoretus (Basilicus)? LATICOsTATUS (Green Sp.) Pl.1.E. fig. 18. 
Ref. and Syn.—Asaphus laticostatus Green, Monog. cast 13. = Ogygia? radiata Salt. Ap. Ray ed. of 
Burmeister, p. 125. 
Sp. Ch.—Obtusely oval ; cephalic shield obtusely rounded about three times wider than long ; thorax (indis- 
tinctly seen) shorter than the head, of eight very slender segments; axis rather less than two-thirds the width 
of the pleurze, which are nearly straight, slightly bent downwards and, backwards at the tip; pygidiwm nearly 
semicircular, length rather more than half the width, and about one-third longer than the thorax; avis flattened, 
undefined at the end, the axal furrows converging most at about the ninth furrow, and then slightly diverging, 
of ten distinct and about four very faint terminal segments, sides gently convex, of nine broad, convex, simple 
ridges, ending in a wide, flattened, simple margin. Length of pygidium from nine lines to two inches. 
The pygidium of this species strongly resembles (as Green remarks) the A. Hawsmanni of Brongniart, but 
has much fewer segments: our large specimen from Maen Goran exactly agrees in size and all characters with 
Green’s cast; the small perfect specimen has much the habit of Bronteus. Mr Salter probably overlooked 
Green’s species when he proposed it as new, and his reference of it to Ogygia is negatived by the simple (not 
duplex) lateral ribs of the pygidium. 
“This is the species referred to in Prof. Sedgwick’s papers as O. Buchi, from the Bala limestone.”—Salter 
in letter referring to our fig. 18. 
Position and Locality —Limestone of Rhiwlas, Bala Lake, Merionethshire; schists of Maen Goran, 
Llangollen ; Black shale, near Builth, Radnorshire (in a newly-opened trial-pit for coal.) 
Explanation of Figures.—P). 1. B. fig. 18. Small nearly perfect specimen, natural size, from Rhiwlas.—Fig. 
18a. A very large pygidium, natural size, from Maen Goran. 
Isoretus (Basilicus) Powis (Murch.) 
Ref. and Syn.—Asaphus Powisi Murchison, Sil. Syst. t. 23. f. 9. =A. elevatus Salter in Ray ed. of Burmeister, 
p. 125. 
Sp. Ch.—Axis of the pygidium as long as the thorax, width slightly less than twice the length, nearly 
semicircular, with the sides slightly straightened; axis rapidly tapering two-thirds the width of the side at the 
anterior margin, less than half that width at the middle, segmental furrows almost obsolete, except the first one ; 
lateral lobes with about eight broad, simple radiating furrows, the radiated portion gently convex, surrounded 
by a flattened, less steeply inclined margin of equal width all round (about one-third the anterior margin); this 
is only crossed by the first or strong articular furrow; axis of the thoracic segments nearly one-third wider 
than the pleurze, gently convex in the middle, abruptly flattened towards the two ends (so as to form, when 
connected, a narrow flattened band on each side of the middle portion), middle portion corresponding in width 
to the anterior end of the pygidial axis; plewrw each with a very strong facet, and wide diagonal pleural furrow, 
truncated at the end. Average length of pygidium one inch nine lines. 
The head supposed to belong to this species has the portion within the eye-line flattened, truncate in front, 
sides nearly straight, diverging slightly to the eyes, from whence on each side it turns abruptly outwards, parallel 
with the posterior margin, then gently arching nearly to the lateral angles; a sharp segmental furrow a little 
in advance of the straight posterior margin; two slightly converging, shallow axal furrows extend from the 
posterior margin towards the front, obscurely defining an oblong glabella. 
The specimens I have examined of the body and pygidium of the Asaphus elevatus (Salter) only differ in 
a slight lateral compression (I should think mechanical); but, as far as I can see, there is no real difference of 
proportion, or any other character, if a slight allowance of this kind be made. 
Position and Locality. —Llanwddyn in the Berwyns (in limestone) Bryn Eithin, Penmachno, 8. of 
Mathyrafal, Montgomeryshire ; Ravenstone Dale, Westmoreland; Pen Cerrig, two miles N. of Builth, Rad- 
norshire; Alt yr Anker, Meifod, Montgomeryshire. 
