STOMAPODA. 389 



land. Others, again, are littoral in their habits, or frequent 

 the sea. 



The oldest known Isopod is a large form which has been 

 described by Dr Henry Woodward from the Devonian rocks 

 under the name of Prcearcturus. It is believed to resemble 

 the living Arcturus Baffinsii. From the Carboniferous rocks 

 we have various forms which may be Isopodous, but the 

 true affinities of which are rendered doubtful by the fact that 

 the condition of the eyes has not been accurately deter- 

 mined. The most important of these is the genus Acantho- 

 telson, of the Coal-measures, in which there are seven thoracic 

 and seven abdominal segments, with apparently six pairs of 

 thoracic legs, and with a pointed telson, flanked by two 

 caudal stylets. Another Carboniferous genus, of dubious 

 position, is Gampsonyx, which combines characters of the 

 Amphipoda, Isopoda, and Stomapoda, but which is stated by 

 Dr Anton Trie to have sessile eyes, and which, therefore, 

 would seem to be referable to one 

 or other of the two first-named of 

 these groups. In the Upper Oolites 

 (Purbeck beds) occurs the Archce- 

 oniscus Brodiei (fig. 244), often in 

 large numbers. In the Chalk 

 occurs the genus Palcega, which 

 ranges to the Miocene Tertiary. 

 Lastly, several forms, some of which 



, f^> i Fig- 244. Archceoniscus Brodiei, 



are of very uncertain affinities, have a fossil isopod from the upper 



been described from the Tertiary Oolites ' 



rocks. 



DIVISION B. PODOPHTHALMATA. The members of this 

 division are Malacostracous Crustaceans, in which the eyes 

 are compound, and are supported upon movable stalks or 

 peduncles, and the anterior portion of the body (cephalo- 

 thorax) is protected by a carapace. In this division are in- 

 cluded the two orders of the Stomapoda and Decapoda. 



ORDER STOMAPODA. 

 Stalk-eyed Crustaceans in which there are generally from six 



