GYP RID IN A DJfi. 
483 
OSTRACODA. 
Lsr the order called Ostracoda — a term derived from a Greek word, signifying a shell — 
the cuirass is in two parts, and incloses the animal like a bivalve shell. The hind jaws are 
furnished with gills. In the family of the Cypridse, the upper pair of antennae are long, have 
numerous joints and a pencil of long filaments ; the lower pair are short, thick, and used as 
feet. There are two pairs of real feet. One of these creatures is called Cypeis. It belongs 
to a genus which has many European species, and it may be found in almost every pond or 
ditch. The body is inclosed thoroughly in its valved cuirass, something like a walnut in its 
shell, the fringed antennae and legs protruding from between the valves and permitting the 
creature to move. It is a most elegant little being, the shell being gracefully curved, and the 
antennae being fine and transparent as if they were threads of glass. Dr. Baird tells us that 
the valves are very brittle, and that on their exterior they are washed with a kind of var- 
nish which protects them from the action of the water. Owing to this varnish, these 
creatures cannot venture even to rise to the surface ; for as soon as the shell is exposed 
to the air, it becomes quite dry, and so buoyant, that no exertion of the Cypris can sink 
it again. 
These tiny animals will often live through a hot summer which dries up the pond in which 
they reside, and at the first rain will make their appearance again, swimming merrily about as 
if nothing had happened. As soon as they feel themselves being deserted by the water, they 
bury themselves deeply in the mud, and even their eggs retain their vitality, though the mud 
should be baked quite hard. When the Cypris changes its skin, it throws off the whole shell, 
the internal parts of the body, the beautiful comb-like gills, and the tiny hairs which clothe 
the bristles of the antennas. 
Two other examples of this pretty genus are named Cypris clardla and Cypris mdua. 
In the family of Cyt.heridas, the upper pair of antennae have no long filaments. 
The members of the typical genus Cythere are mostly marine, and may be found in the 
little rock-pools at the sea-side, darting about among the branches of sea-weeds and zoophytes 
that live so plentifully in such situations. Safe in these sheltered spots, they care nothing for 
wind and waves, and the storm which flings the huge whale on the shore will fail to injure 
these tiny beings, whose very minuteness is their safety. One species, Cythere minna , is 
remarkable for being the largest one seen by Dr. Baird. Its valves are white. It was found 
in deep water and taken in a dredge. Cythere inopinata derives its specific name of inopinata 
or unexpected, from the fact that the creature was found where no one would have expected 
its presence, namely, in small ponds. It is a very small species, and always remains at the 
bottom. Its color is white, and there is a little orange-colored mark on the upper edge. An 
oblique view of this species has been chosen, in order to show the curious rounded projections 
upon the middle of each valve. 
The Cythere impressa was found in sand at Torquay. The shell is dull black in color, 
and is covered with little punctures impressed upon its surface, whence is derived its specific 
name. 
A closely allied genus is remarkable for the manner in which the valves are ridged, 
irregular, covered with tubercles, and having their edges boldly toothed. This species was 
taken in the Isle of Skye. 
In the family of the Cypridinadse there are two eyes, set as footstalks, and two pairs of 
feet, one pair being always within the shell. There is only one genus of these creatures, and 
all the species are marine. The shell is oval, sharply pointed at each end, and the front edge 
is deeply notched. The pair of feet that are retained within the shell are modified into one 
organ, which seems to be intended for the purpose of supporting the eggs. Some other 
species are luminous. 
