2G 



Guide to Crustacea. 



Table-case primitive characters. In the large number of the somites and the 

 No. 1. uniformity of the hmbs, as well as in some points of internal 

 structure (heart, nervous system) they approach more closely 

 than any other living Crustacea to the hypothetical ancestral type 

 of the Class. In some respects, however, such as the reduction of 

 the mouth-parts, they are considerably specialized. 



The order includes three Sub-orders (sometimes ranked as 

 Orders) the members of which differ widely in external appear- 

 ance. They are found in fresh water or in brine pools. 



Ajiua cancriformis, from Kirkcudbrightshire, slightly enlarged. 

 [Table-case No. 1.] 



In the Sub-order Anostraca there is no carapace and the 

 animals have a more worm-like appearance than is usual in 

 Crustacea. 'The eyes are set on movable stalks. The males are dis- 

 tinguished by the remarkable development of the antennae, which 

 form complicated clasping organs for seizing the females. This is well 

 shown in the specimen of Streptoccplialus rubricaudatus exhibited. 



In the Sub-order Notosteaca the carapace forms a broad 

 dorsal shield, resembling, at first sight, that of the Arachnidan 

 King-crabs. Apiis canerifonnis (Fig. 7) is found in fresh-water 



