some British Fossil Crustacea. 4.09 
Not uncommon in the black Wenlock shale of Pen Cerrig, 
Builth. 
(Col. University of Cambridge.) 
Barrandia (M‘Coy), n. g. 
Gen. Char. Body ovate, depressed ; cephalic shield semicircular, 
with the lateral angles produced backwards 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 ; eye-line behind the eye cut- 
ting the posterior margin about the middle, in 
front of the eyes arching forwards, first out- 
wards and then inwards; thorax of seven seg- 
ments ; axis convex, nearly as wide as the pleuree, 2arrandia. 
tapering towards the pygidium ; plewre flat, their ends slightly 
faleate and bent backwards, no facets, a slightly oblique sub- 
mesial pleural furrow not quite reaching the end; pygidium 
semicircular, entire, having very few simple segmental furrows 
placed near the anterior margin (one to three in number) ; 
axis 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 deserip- 
tion 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 A/ceste is figured by those authors 
with three segmental furrows to the pygidium, while this has only 
one, making the total 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 sup- 
posed to be constant. I know but one species, the following*. 
Barrandia Cordai (M‘Coy). 
Sp. Char. Length one-fourth more than the width, length of 
* Since the above was written Mr. Salter has figured (2nd Decad. Geol. 
Surv. pl. 7. f. 4) a species of this genus, with three segments to the pygi- 
dium, which he gives without any apparent reason as the young of an Irish 
species of Ogygia (O. dilatata, Phil., O. Portlochki, Salt.). My reasons for 
dissenting from this view are, Ist, it is contrary to analogy of other allied 
Trilobites to suppose that the young and adult differ in the number of their 
thoracic segments ; 2nd, in the Cambridge collection, specimens of the Ogy- 
gia Buchi, half an inch wide, have exactly the same number of segments 
and other characters as an adult six inches long; 3rd, the supposed young 
has only been found at Builth, where the Ivish species, his supposed adult 
thereof, has never been found, being only known in the schists at Waterford, 
where it abounds, but where the supposed young have not occurred. 
