SIT Aim AN TRILOBITES. 
3 
LOWER SILURIAN ROCKS. 
CRUSTACEA.—Trilobitcs. 
There are no less than eight species, all, except one, belonging 
to ordinary European genera; and the forms are very like those 
in our own slate rocks. The very first species we notice would 
alone indicate the Lower- and not the Upper-Silurian rocks; 
the gyius Asaphus never being known to rise so high as 
these, while Cheirurus, Spheerexochus, Cah/mene, Illanus, all 
of which genera occur in the collection, are as common in the 
lower as in the upper division. All are essentially Silurian, 
except Cheirurus , which is' also known in the Devonian 
rocks. 
1. ASAPHUS EMODI- 
Plate 1 , figs. 1-9. (Fig. 3, var. brevior.) 
A. capite bi’evi. Glabella distincta pyriformis convexa, sulcis 
utrinque binis exaratis,—anticis obliquis, posticis rectis. Labrum pro- 
funde impressum. Pleurae convexiusculae. Cauda semicircularis, sub- 
plana, axi longo annulato, piano nisi ad apicem convexiori; lateribus 
6—sulcatis, sulcis brevibus ; margine latissimo. 
It is possible that we have two species figured under this 
name; for the proportions of the glabella in fig. 3 are rather 
shorter, and the outline of the labrum in fig. 5 is longer than 
that of the more common one (fig. 4). Nevertheless, as the 
materials are imperfect, it is not worth while to separate 
them. .If better specimens be found, the short-headed speci¬ 
men (fig. 3) may then be described as a new species. The 
specific name is intended to ajrply first to the caudal shield, 
figs. 8, 9. 
The head must have been rather short, and the glabella 
convex for the genus, pear-shaped, slightly apiculate in front, 
and furnished below with two pairs of deep furrows. The 
upper pair are very oblique, the lower pair (which are really 
an incomplete nuchal furrow) run direct across. In the shor¬ 
ter variety (or species), fig. 3, the glabella is flatter, and the 
