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PROCEEDINGS OE SOCIETIES. 
glabella, having* three ridges extending to about two-thirds of the breadth 
ofithe shield, rounded at their anterior extremity, and forming correspond¬ 
ing depressions, the central ridge being broader at the posterior extremity, 
the two outermost ridges curving at about half their length towards the 
very slightly raised semicircular eyes, and continuing beyond the poste¬ 
rior extremity of the shield in two sharp, straight spines, which project 
over the abdomen one-tenth of an inch. The cephalic shield is also pro¬ 
duced into a longer spine at the posterior angles, three-tenths of an inch 
in length, which spreads out on either side from the body. There appears 
to be a facial suture, commencing at the anterior margin, curving towards 
the eye, and forming a half circular lid, although it is not perceptible 
beyond this point. The abdominal and caudal extremities are wanting. 
Size of cephalic shield, breadth, 7-10ths of an inch. 
,, ,, 3j-10ths ,, 
This species is closely allied, in the form of its cephalic shield, to 
Limulus trilobitoides , figured by Buckland in his ‘ ‘ Bridgewater Treatise, ’ ’ 
Plate xl vi., Pig. 3 ; and by Prestwich on the “ Geology of Coalbrook- 
dale,” in the “ Geological Transactions of London,” second series, vol. v., 
Plate xli., Pig. 8. 
Portlock, in his “ Eeport on the Geology of Londonderry,” &c., 
figures at Plate xxiv., Pig. 11, from carboniferous shale, Maghera, Derry, 
a specimen which he refers, although somewhat doubtful, to this species; 
his figure is destitute of spines, and certainly does not appear to bear 
much resemblance to the species in question. 
There are, however, differences in the specimen under notice which 
are not exhibited in the figures before alluded to, sufficient to make it a 
new species. These consist in the two outermost ridges, defining the 
central part of the cephalic shield or head, being continued over the ab¬ 
dominal segments as spines, and in the great spreading out of the two 
longer spines at the posterior angles of the shield; as well as in possess¬ 
ing a distinct facial suture. 
The great interest attached to this specimen is in the fact of the rare 
occurrence of remains of this genus in Ireland, and its evident affinity 
with similar forms of Crustacea from the lower coal-measures of Coal- 
brookdale, a formation believed to be of estuary origin, and described by 
Mr. Prestwich as consisting of alternating beds of sandstone and clay, 
the strata being between 700 and 800 feet thick, which has yielded be¬ 
tween forty and fifty species of terrestrial plants, many species of Mol- 
lusca, besides fishes of the genera Megalichthys, Holoptychius, and 
others, as well as several species of the remarkable Crustacea before al¬ 
luded to; the specimen now brought before your notice being also found, 
under somewhat similar conditions, associated with several species of 
plants and Mollusca. 
The following species are now included in the new genus Steropis:— 
Steropis arcuatus (Baihj), n. s. Coal-measures, Bilboa Colliery, 
county of Carlow. 
