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salt water. The Artemis inhabits only the Lymington salt-pan, in water 
holding a solution of 25 per cent, of common salt. 
The valves of the Entomostraca are often sculptured with exquisite 
reticulations, striations, or other designs. They differ from the shell of a 
Mollusc by the absence of lime, and rather resemble the elytra of beetles 
by being composed of a substance resembling chitine. When lime is 
present the carapace effervesces with an acid and reddens by boiling like 
that of a lobster. 
The bi valve carapaces of the Cyprididae and Cytheridae are united at the 
dorsal margin by a ligamentous hinge. The carapaces are always 
inequivalve, the left valve being always the larger in every species except 
Bairdia, Siliqua, and Cytherella, where the right valve is the larger one. 
The carapace of a Lobster or Crab is formed by the development of the 
tergal pieces, while that of an Entomostracon is formed by the development 
of the epimeral pieces. In most fossils the carapace, valves, or tail-spines 
are the only portion preserved, and of those most frequently the exuviae 
only. 
The author then proceeded to give a general sketch of these fossils and 
their mode of distribution. 
1st. The Cambrian and Silurian periods. These deposits are frequently 
very rich in specimens, as Hymenocaris from Dolgelly and Tremadoc, while 
from other places are obtained Pterygotus, Eurypterus, Ceratiocaris, 
Trilobites, Beyrichia, Leperditia, and Dithyrocaris. The Beyrichia is a very 
distinctive fossil in the Silurian beds, B. tuberculata marking the Upper 
Silurian while B. complicata points out the Lower. 
The Trilobites having been fully considered at a previous Meeting, Mr. 
Stoddart passed to 
2. The Devonian period, which although less rich in fossil remains yet 
furnishes very large Pterygoti, Trilobites, and Leperditiae. The latter 
chiefly occur in some of the Petherwyn and Marwood beds, which appear 
to belong more properly to the Carboniferous system. 
3. The Carboniferous period saw the last of the Trilobites, but as a 
compensation tbe water swarmed with Cyprididae and Cytheridae, the 
former of which inhabit fresh and the latter salt water. After rather 
minutely describing the anatomical difference between a Cypris and Cythere, 
specimens were shewn from 
4. The Permian and Triassic systems. In the Permian first occurs the 
genus Bairdia, which has no hinge teeth or crenulated margin to the valves 
of the carapace. In the Triassic strata abound the little Estheriae. 
