92 GUIDE TO THE FOSSIL INVEHTEBKATE ANIMALS. 
Gallery 
VIII. 
W all-case 
13c. 
Table-cases 
23-20. 
Wall-cases 
13 & 12. 
part in biting ; the four other pair.s are solely for walking. 
The breathing organs were probably lung-books, as in 
Scorpions and Opiliones, but there is still little evidence on 
this i)oint. The Araneae or true spiders are also found 
among Carboniferous fossils ; some from Bohemia are shown. 
These and other orders of Arachnida are, however, not very 
richly represented in the rocks until Cainozoic times, when 
they are met with in the Oligocene of the Isle of Wight 
and of Florissant in Colorado, in the lignites of Rott near 
Bonn, the ftliocene of Oeningen in Baden, and in the Baltic 
amber. 
Class CRUSTACEA. 
These are almost till dwellers in water, breathing by gills. 
Their outer chitinoiis envelope is more often thickened by 
lime than is the case in the Classes previously described, and 
this crustaceous nature combines with their habitat to render 
them fairly common fossils. The annexed figure of a fossil 
lobster (Fig. 45) shows that in the more typical forms the 
Fig. 45. — A tj-pical Crustacean ; one of the Macrurous Decapods, Glypluia 
regleyatia, of Oxfordian age. a-h, bead ; b-c, thorax, covered by the 
carapace ; c-d, abdomen, bearing a telson, e, and tail-fins, / ; gf, oye , 
h, i, limbs of the head; fe-o, walking limbs. Two-tbirds nat. size. 
(From Woods’ “ Palaiontology,” by permission of the Cambridge 
U n i versity^Press.' 
envelope^ is composed of segments, in which an upper and 
under half are clearly distinguished. Several front segments 
are joined together and covered by a shield, part of which 
projects backwards as a carapace, and from the number of 
limbs borne by this part of the body the number of segments 
may be estimated ; in the lobster, for instance, it is thirteen 
(not all preserved in the fossil figured). The six remaining 
segments form the abdomen, at the end of which is the 
telson. In the number of the body-segments, in the niannei 
