PLATE 45, 45*. 
hinder part of the shell lunate : the angles very acute. The 
tail or posterior part of the body straight, rounded, and con- 
siderably less than the crescent-shaped covering from which 
It proceeds. It is divided by segments, somewhat similar 
to those on the back of E. derbyensis, and terminated by an 
undivided, subulate style, equal in length to the rest of 
the tall. 
I am Sony, the rareness of this tossil in Derbyshire pre- 
vents me from giving *a more accurate description. The 
specimen figured is in a nodule of ironstone ; it was found 
in argillaceous strata along with vegetable petrifactions, on 
die borders of the county, I believe near Mansfield, and 
IS the only one I have yet seen. It is not very perfect ; but 
sufficiently so to determine its specific difference from the 
Entomolithus before described. To this I have little to 
add, except, that the original appears to have approached 
nearer in size and figure to the Monoculus Apus, than to any 
other known recent species of that genus. Another note of 
agreement is its having been a fresh water, and not a 
marine insect, if we may judge by the strata, in which the 
fossil occurred, and the petrifactions with which it was 
accompanied. 
FIG. 3 . T. 45 . 
A magnified portion of E, M. fiustriformis described at 
Tab. 43. Fig. 1, ‘2. 
