Crustacea. | LOWER PALAZOZOIC ARTICULATA, 149 
OGyGIA RADIANS (Coy). PI. 1. F. fig. 2. 
Ref—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Sp. Ch.—Pygidium nearly semicircular, slightly convex ; axis conical, undefined at the end, having three 
narrow segmental furrows at the anterior end, lateral lobes with three broad radiating ribs faintly divided 
at their axal ends by a small pleural furrow; margin tumid, entire length four lines, width seven lines. 
I provisionally give this name to a small pygidium not unlike that of the Barrandia Cordai, but 
which from the duplicate lateral furrows belongs more probably to Ogygia, and probably confirmatory of this 
view, I observe in the 2nd Decade of the “Geol. Surv.” t. 7. f. 5, a small eight-jointed true Ogygia from 
Builth, having the pygidium almost identical with the present species, if, as I suspect, the duplicating 
furrows have been accidently omitted in the plate (the figure alluded to is given as the probable young 
of the Ogygia dilatata (Phill.) which abounds in the schists at Waterford). 
Position and Locality —Not uncommon in the black shale of Pen Cerrig, Builth, Radnorshire. 
Explanation of Figures.—P\. 1. F. fig. 2. Pygidium natural size, from the black shales of Pen Cerrig, 
Builth —Fig. 2a. The same magnified to shew the fine duplicating furrows, as in Ogygia generally. 
Genus. BARRANDIA (M°Coy). 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Gen. Char.—Body ovate, depressed ; cephalic shield semicircular, with the lateral angles produced back- 
wards into short spines; glabella widely clavate, the axal furrow strong and nearly parallel at the base, 
becoming obsolete towards the front; eyes large, narrow, reniform; e¢ye-line behind the eye cutting the 
posterior margin about the middle, in front of the eyes, arching forwards, first outwards and then inwards ; 
thoraw of seven segments; axis convex, nearly as wide as the pleur, tapering towards the pygidium ; 
pleurze flat, their ends slightly faleate and bent backwards, no facets, a slightly oblique submesial pleural 
furrow not quite reaching the end; pygidiwm semicircular, entire, having very few simple segmental furrows 
placed near the anterior margin (one to three in number) ; ais short, having one to three small segmental 
furrows. 
This I conceive to be a subgenus of Ogygia, from which it differs in its fewer thoracic segments, and 
having but very few and simple ribs to the tail. The genus agrees with the description given by Hawle 
and Corda of their genus Alceste, with the exception of this having seven thoracic rings, and that having 
but four—it is remarkable that AJ/ceste is figured by those authors with three segmental furrows to the 
pygidium, while this has only one, making the ¢ofal number of segments visible the same in both; the 
number of the pygidial segments, is, however, of course, liable to vary with the species, while the thoracic 
ones are allowed to be constant. 1 know but one species, the following. Since the above was written, Mr 
Salter has given a figure (2nd Decad. Geol. Surv. Pl. 7. f. 4) of a species of this genus, with three seg- 
ments to the pygidium, which he gives without any apparent reason, as the young of an Irish species of 
Ogygia (O. dilatata Phill. = O. Portlocki, Salt.) My reasons for dissenting from this view, are, Ist, it is contrary 
to analogy of other Trilobites to suppose that the young and adult differ in the number of their thoracic 
segments; 2nd, in the Cambridge Collection, specimens of the O. Buchi, half an inch wide, have exactly the 
same number and character of segments as adults, six inches long; 3rd, his supposed young has only been 
found at Builth, where the Irish species (his supposed adult thereof) has never been found, being only known 
in the schists of Waterford, where it abounds, but where the supposed young has not occurred. 
BARRANDIA corDAI (M/‘Coy). Pl. 1. F. fig. 1. 
Sp. Oh.—Length one-fourth more than the width; length of head, thorax and pygidium almost equal ; 
cephalic shield slightly more than twice as wide as long, lateral angles very short; eyes half their length 
from the axal furrows; pygidium depressed, length rather more than half the width, axis two-thirds the 
length, conical, segmental furrows obtuse. Length eleven lines. 
