60 REPORT—1852. 
deeply furrowed, their ends rounded or truncate. Tail small, the axis short of 1 
segment, the sides without furrows. 
The position of the very minute eyes is indicated by a slight indentation opposite 
the front of the glabella; they must have been linear and small, for there is no visible 
elevation or appearance of an eye-lobe. In this respect there is some difference be- 
tween the form under description and the North American genus Triarthrus, to 
which it is, nevertheless, most closely allied. In both genera the eye-line takes the 
remarkable course above described, viz. in an oblique and almost marginal line from 
the front to the outer edge of the narrow cheeks, and the furrow which runs along 
the posterior margin of the cheeks in both genera turns upward towards the termi- 
nation of the facial suture. Tvriarthrus, too, has the ends of the thorax segments 
rounded or square, not pointed and recurved as in other Olenoid genera. But the 
present genus differs in the gibbous form and inflated glabella without lobes, as well 
as in the fewness of the segments of the thorax, 7 instead of 15 or 16. 
Species 1. C. socialis, n. sp. Length about a quarter ofan inch. Locality. Chair of 
Kildare, in Lower Silurian. 
Acidaspis, Murchison. 
Of this remarkable genus, one new Irish form has to be added to the list.. It was 
formerly (Mem. Geol. Surv., vol. ii. p. 1. pl. 9. fig. 5) considered by me the same 
with A. bispinosus, M‘Coy, a species distinguished by the possession of two spines 
on the neck. Many species are now found to have this character. The original 
one, described by Prof. M‘Coy, is a minute species with a remarkably inflated 
glabella, and a sinuated front. It is from the Chair of Kildare. 
The new species, of which good specimens occur in Waterford (Lower Silurian), 
has a wide and somewhat depressed head, with a straight front, and the glabella 
lobed, and not inflated. It will be figured and described in Decade 7 of the Me- 
moirs of the Geological Survey as 4. Jamesii. 
4figlina, Barrande. Cyclopyge, Corda. 
This genus, proposed by Barrande to replace the name gle, which he formerly 
bestowed on it, exhibits the greatest proportional development of the eyes known 
in the group of Trilobites. They occupy the entire side of the head to the exclusion 
of all other parts of the cheeks, and meet in front (as in the case of many insects, 
especially of the male sex). In this respect Remopleurides of Portlock is the only 
genus that can be compared with it; the genus under notice, however, has the eyes 
greatly more developed, and with large lenses quite visible to the naked eye; few 
body segments, and a rounded tail. The genus must for the present be placed near 
Asaphus. Two or three species are known in Bohemia, all Lower Silurian. 
A new one, 4. mirabilis, has been found at Portrane, Dublin; and the same, or an 
allied species, in Anglesea and South Wales. It will be figured shortly in Decade 7, 
Mem. Geol. Survey. 
Remopleurides, Portlock, 
As this has just been quoted, it may be well to say, that perfect specimens of #. 
dorsospinifer, Portlock, will also be figured with the above. The remarkable dorsal 
spine, detected by the discoverer of the genus, is very likely a character peculiar to 
the male sex, and it is more than probable that R. Colbii is the female of the same 
species. Such appendages characterize the male sex in Spheroma. 
In the Remopl. dorsospinifer, the possession of this spine, on the 8th segment, is 
accompanied by a general narrowness of form as compared with FR. Colbii, but besides 
this, there is no available means of distinction. Col. Portlock had himself suggested, 
that two or more of these forms might prove to be varieties of one species, and in 
this, after careful examination, I fully concur. Again, except in the possession of 
the lateral appendages (which might be expected in the mature ovigerous female), 
and in a still greater breadth of form, A. laterispinifer does not differ from 
the two above mentioned. And hence these three forms may be respectively regarded, 
as the male, and the young and mature female forms of the same species. While 
suggesting this as probable, and supported by general analogy among the Crustacea 
and other articulate tribes, it would not be advisable to alter the names originally 
given. 

