SYNOPSES OF NORTH-AMERICAN 
INVERTEBRATES. 
V. FRESH—-WATER OSTRACODA. 
Cc. H. TURNER. 
Tue Ostracoda form a well-defined division of the Ento- 
mostraca. They resemble the Lamellibranchiata in having the 
body enclosed in a bivalve shell. This peculiarity, which 
causes many a novice to mistake the Ostracoda for small 
Mollusca, is merely a superficial resemblance; for, although 
the structure of the enclosed animal is quite primitive, yet it 
is decidedly crustacean. 
The body always bears seven pairs of articulated appendages. 
The first five of these are head appendages; but, in differ- 
ent groups, either one or all of the last three pairs of these 
cephalic appendages may be modified for locomotion. The last 
two pairs belong to the body and are usually known as feet. 
In some cases (Cypris), however, the last pair of feet is not 
used for locomotion. In most cases the abdomen terminates 
in a pair of appendages which resemble legs. 
Handicapped by a comparatively heavy shell, the Ostracoda 
make, as a rule, very poor swimmers. Near the surface in 
deep waters these creatures are rare. Shallow ponds and 
marshes are their favorite haunts, but they are also found in 
rivers and at or near the bottom of lakes. Comparatively 
speaking, some forms swim quite well (Cypria, Cyclocypris, 
Cypridopsis), while others do not swim at all, but creep along 
the bottom or up the stems of plants, or else burrow in the 
mud or sand (Erpetocypris, Candona). 
In the South, specimens may be collected at almost any time of 
the year, but the spring and fall are the best collecting seasons. 
In the North they may be collected from early spring to late fall, 
but spring and fall seem to be the best collecting seasons. 
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