CRUSTACEA. SCHIZOPODA 323 



Silurian. Echinocaris is found in the Devonian ; and 

 Dithyrocaris in the Carboniferous. One genus (Aspido- 

 caris) has been recorded from the Trias. 



ORDER II. SYNC ARID A 



The Syncarida are a small group of primitive Mala- 

 costraca, the living representatives of which are found in 

 fresh water in Tasmania and Victoria, and belong to three 

 genera of which the best known is Anaspides. The body 

 is elongated and without a carapace, and is remarkable 

 for the fact that all the thoracic segments are distinct. 

 All the thoracic legs are similar in general character, and 

 all, except the last one or two, are biramous ; their coxo- 

 podites bear externally two rows of plate-like gills, but 

 these have not been found in fossil specimens. The 

 abdomen is large, and the first five pairs of appendages 

 consist of long, many-jointed exopodites and small endo- 

 podites ; the appendages of the sixth segment form with 

 the telson a tailfin. 



Fossil representatives of the Syncarida are found in 

 the Carboniferous and Permian deposits, and belong to 

 the genera Prceanaspides, Palceocaj'is, Acanthotelson, and 

 Uronectes (= Gampsonyx). These appear to be closely 

 allied to Anaspides. 



ORDER III. SCHIZOPODA 



The Schizopods (fig. 141) are small Crustacea in which 

 the thorax is more or less completely covered by a well- 

 developed, but thin and usually flexible, cephalo-thoracic 

 shield. The eight pairs of thoracic legs are generally 

 biramous and, unlike those of the Decapods, are all similar 



21—2 



