PLATE 45. 45*. 
surface of the head are nearly of a triangular form : each 
furnished, near the centre, with a large lunated tubercle ; 
discovering, in perfect specimens, a reticulated structure, 
like that of the eyes in living insects, when magnified. 
The back of the insect is composed of strong, convex, tri- 
arcuate segments ; their number varying from twenty to 
twenty-four ; each marked with a line of very minute 
tubercles. The middle parts of the segments are more 
elevated than those on each side, and form collectively, 
down the back, a keel-shaped prominence, which ends 
somewhat obtusely, before it reaches the margin of the tail. 
The segments of the keel directly transverse, those on each 
side, particularly near the tail, somewhat oblique. The 
tail obtuse, entire, and destitute of any appendage. 
The above described parts are all that are ever present in 
the fossil. — And as the under side is constantly filled with 
the stone which constitutes the matrix, it would be impos- 
sible to examine the legs and inferior parts of the abdomen, 
did they remain, which it is evident, however, they do 
not ; the petrifaction being formed merely from the upper 
shell, or covering of the back and head. 
This fossil is not frequent in many parts of the county. 
It is principally met with in the black marble at Ashford, 
where it very rarely occurs in a perfect state ; the head and 
body being found, for the most part, separate from each 
other. The prototype appears to have been a gregarious 
