THE CYPRIS AND ITS FOSSIL ANCESTORS. 81 



because they are natatory pelagic that they are so widely dis- 
tributed. 
Now we have stated that the chief economy in nature of the 
fresh water Cypris was the removal of dead animal matter, and 
there is every reason to believe that the same offices are per- 
formed by the marine forms, especially those that live far from land 
where little else than animal matter could reach them. 
Having taken a sketchy view of the anatomy and geographical 
distribution of our little friend, and having seen by such wide 
spread distribution how greatly it works to assist in keeping down 
the deleterious results of organic decay at the present time, and 
having also seen that his valves or shells are conspicuously present 
in the mud and sands of the existing seas and lakes, let us see 
whether the rocks, representing the deposits of former seas and 
lakes, and lands, reveal to the taps of hammers aught upon the sub- 
ject, 
Of course it is known to most readers of the Worthern Micros- 
copist that the stratified crust of the globe is divided into certain 
“formations.” To get an insight into the ancestral line of the 
Cypridian family, it is necessary to note the table of the principal 
formations of these stratified rocks, which are as follows—reading 
them from the newest to the oldest :— 
TERTIARY OR CAINOZOIC MPIGIOSE IMCL t-vthx,ics eis ccooe'os 


Cretaceous... fissch.al ae 
Weealdens.14sc5. ee ee 
Purbeck +) Asch suey 
Oohtie 22S see 
LiassiC inate 



SECONDARY OR MeEsozo1c 




(Pettiiianeei ets cee 
Carboniferous: A. aan 
Devonian or Old Red... 
| Upper Silurian. vas..eas 
: Lower, Silurian +298 
| Upper Cambrian......... 
eae Cambrranrivits..: 


PRIMARY OR PAL#OZOIC 
iB chgacioticme Sl ey pean 
