84 THE NORTHERN MICROSCOPIST. 


came one of the most important order of the Crustacea at this 
period, because, upon scrutiny, we find that of all Crustacean 
orders the Ostracoda is most prominent. ‘The following compari- 
son will show how important this little fellow has become. In the 
Silurian seas the ‘Trilobite numbered nearly 320 species, and the 
Ostracods not more than 4; now, in the Carboniferous the Ostra- 
coda number 85 genera, and the Trilobite only 3. It may be noted 
here that as the Trilobitas became extinct in this formation at an 
early perlod—namely the Carboniferous Limestone—it is just pos- 
sible that the marine forms of Ostracoda, as survivors, had better 
opportunities for surviving through the extinction of the Trilobite. 
This will also apply to those found in the higher Carboniferous 
rocks, where the Cypris itself is found fossilized in great quantities 
in the Burdihouse Limestone and in the black shales of the Scotch 
coal measures. ‘The fossilized forms of the Cypris in these sand- 
stones and shales present a singular appearance zz sz¢u, and would 
indicate that the shale represents a dark muddy shore of an 
estuarine character. 
Leaving the Carboniferous formation, the next in order is that 
of the Permian, before alluded to as representing the first break in 
the column, and consequently the close of Palaeozoic rocks. 
Passing the Triassic rocks, in which are carried through the 
Cypridean forms, we may just notice the fact that in the Liassic 
rocks the Cypris is found fossilized amongst the fossil bones of the 
animals which lived in those seas. What clearer proof can we 
have than this that the functions of the Cypris then, as now, were 
to eat up dead animal matter. The simple history of which de- 
posit has been that some unfortunate Ichthyosaurus or other 
saurian of those waters has got stranded by venturing too far up 
the river into some tidal pool,—has died,—and then the Cypris, 
amongst other such busy little bodies, have begun their work of 
eating up the creature, when, probably, lo, suddenly has come 
down, from some short distance up the river, a flood so heavily 
laden with some muddy sediment as to enshroud both saurian 
and crustacean so completely as to entomb them, to be in after 
ages revealed in fossil form, and record the fact to enquiring 
man. : 
That the Cypris also existed in other than marine waters is re- 
corded by the fact that in Gloucestershire they are found in the 
fresh water or estuarine deposits of the Lias, in a shale overlying 
the well-known “ Insect-beds.” 
Although we can find no record of any special prominence of the 
Cypris in the Oolites, yet they undoubtedly existed where the circum- 
stances were favourable, because in the succeeding Purbeck and 
Wealden beds we find them at their maximum, but in such a changed 
form from the Silurian types as to call for special note. Now, the 
