92 GUIDE TO THE FOSSIL INVEETEBRATE ANIMALS. 



Gallery 

 VIII. 



Wall-ease 

 13c. 



articulated to the fore-part, and consists of flexibly joined 

 segments. As in typical Arachnida the month is at the 

 front of the body, and only the first two pairs of limbs take 

 part in biting ; the four other pairs are solely for walking. 

 The breathing organs were probably lung-books, as in 

 Scorpions and Opiliones, but there is still little evidence on 

 this point. 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 Eott near Bonn, 

 the Miocene of Oeningen in Baden, and in the Baltic amber. 



Class CRUSTACEA. 



Table-eases These are almost all dwellers in water, breathing by gills. 

 23-20. Their outer chitinoiis envelope is more often thickened by 

 13 izl^^ 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 typical Crustacean ; one of the Macrurous Decapods, Glyphea 

 regleyana, of Oxfordian age. a-b, head ; b-c, thorax, covered by the 

 carapace; c-d, abdomen, bearing a telson, e, and tail-fins,/; g, eye; 

 h, i, limbs of the head; k-o, walking limbs. Two-thirds nat. size. 

 (From Woods' "Palaeontology," by permission of the Cambridge 

 University 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 



