ABACII1STDA. 2G5 



To this family belongs the beautiful Astacus, from the 

 neocomian stage of Atherfield, Isle of Wight* (fig. 177). 



FIG. 177. Astacus Vectensis. 



The PALINUHIDJE, PAGURID^;, DKOMID^, LEUCOSIDJE, 

 and G-RAPSID^;, have fossil genera in the oolitic, cretaceous, 

 and tertiary strata. 



The CANCERID^;, or Crab family, are found in a high state 

 of preservation in the eocene clays of Sheppey and in the 

 "Bognor beds at Alum Bay, Isle of "Wight, an'd in strata of 

 the same age in France. 



CLASS IV. AKACHNIDA. 



The Spiders have the head and thorax united and covered 

 by a cephalo-thorax. They have four pairs of feet. The 

 tegumentary skeleton is in general solid ; the higher forms 

 breathe by simple internal sacs or lungs, the inferior forms 

 by trachea. The simple eyes, in general eight in number, 

 are disposed around the anterior part of the cephalo-thorax. 

 We find very few members of this class in a fossil state in 

 the older rocks ; but the presence of Cycloptlialmw, a genus 

 of SCORPIONIDJB in the carboniferous stage of Bohemia, 



* Mantell's Isle of Wight. 



