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of its curve and size it agrees pretty well with Nereites 
Gamhrensis, hut in the shape of the teet it somewhat re- 
sembles Nereites Sedgiuichii of Murchison, so being 
different from both of these species it is proposed to call it 
N'erites Monensis. 
The two small specimens described in plate ii., fig. 2, are 
of irregular oval shape, about three-quarters of an inch long 
and half an inch broad. They occur in considerable numbers 
in some of the beds, but to what they belonged it is difficult 
to say, without they are the open valves of a Linguella or 
some other bivalve shell. 
The occurrence of Nemerites and Nereites, or bodies 
resembling them, in the blue slates, similar to those found 
in the Lower Llandeilo beds at Llampeter, appears to show 
that these Manx schists are of Lower Llandeilo age as 
suggested by Mr. Horne. 
The blue slates in which the specimens of Nemerites and 
Nereites are found, and the beds near Derby Castle, con- 
taining Scolites, from their organic remains, may therefore 
be taken as the Manx representatives of the Lower Llandeilo 
beds ; but what the several thousand feet of strata lying 
above them at Walbury, Douglas Head, and Banke’s Howe 
are, we have at present no evidence from fossils to enable 
us to decide with certainty. From Mary Yeg, and the 
other localities where the blue slates containing Nereites 
and Nemerites are found to the mica schists and gneissic 
rocks, near Foxdale, is fully four miles on the rise and dip, 
and the underlying strata, as far as exposed, incline to the 
S.E. at a high angle ; so, after allowing for faults, probably 
some thousand feet of strata lie under the Lower Llandeilo 
beds. Whether these are all Lower Silurian, or some of 
them Cambrian, remains yet to be proved; but it is appa- 
