82 THE NORTHERN MICROSCOPIST. 
By referring to the preceding diagram, which is based upon a 
similar arrangement prepared by Sir Chas. Lyell, it is seen that 
the column shews upon the left hand side the names of the three 
principal divisions of these formations. These divisions are worthy 
of note as indicating two breaks, illustrative of the remarkable 
change in the fauna and flora at these periods. Upon the right 
hand side of the column is a diagrammatic line, shewing, by its 
attenuations and thickenings the persistency of Ostracoda life and 
the periods during which it most flourished. It will be seen that 
at the present time or ‘recent,’ the existence of it is almost as pro- 
lific as it was during the Wealden and Purbeck, during which 
periods it attained its maximum as we shall hereafter see. In the 
next formation, viz., the Pleistocene, and in the Meiocone and the 
Oolitic and Liassic the genera is held on only by a few species which 
do not shew any prominent features as a strata. This may be 
owing to peculiar conditions of climate at those periods, and also to 
the material of the formations being unsuitable to either the life of 
the animal or to the preservation of its remains. 
In the “Permian” the line is altogether wanting here. We see 
there is a total break, the Paleozoic forms ending abruptly in 
the carboniferous, and the secondary forms, almost as abruptly, 
beginning in the Triassic, and continue without break into the 
Tertiary formations. 
This break may be only apparent for the want of evidence, or it 
may be so in actual fact. We should be inclined to think it is 
apparent only, and that careful research may reveal the “ missing 
link.” Whichever it may be, it is only another instance of the 
great change which took place in both the fauna and flora of those 
periods. 
The earliest records we find in the rocks of the fossil ancestors 
of the Cypris are in the Lower Cambrians, discovered by Dr. Hicks 
in the Solva grits a few months ago. 
Since then, Prof. T. Rupert Jones has worked them out from the 
Wenlock shales of Shropshire in the upper Silurian formations. 
Previous to either of these discoveries being made the earliest 
prominent traces were those so ably recorded by Sir Roderick 
Murchison, as occurring in the Downton sandstones or ‘ passage 
beds,’ existing between the Silurians and old red sandstone. These 
beds have just recently been renamed, and are called the ‘“Devono- 
Silurian beds.” 
The earliest types of the Cypris found in the solva grits of Lower 
Cambrian rocks occur in rocks at St. Davids, and are called 
Leperditia ferruginea and Leperditia Cambrensis, and were most 
probably marine. | 
The next indication we have of its existence is a little higher in 
the scale of rocks—in a member of the Upper Cambrian, viz., the 
