ARTHROPODA. 87 



GROUP B. LEPTOSTRACA. Small marine Crustaceans, with five cephalic, 

 eight free thoracic, and eight abdominal segments; a forked telson. 

 Anterior part of body enclosed in a bivalve shell. Eight pairs of folia- 

 ceous swimming-feet attached to the thorax. Eyes compound, on short 

 stalks. No larval stage. Only known genus, Nebalia. 



The Crustacean head is often regarded as composed of six segments ; the 

 telson is possibly a segment TR. 



