DECAPODA. 



513 



FIG. 314. Male and female of Astacus ftuviatilis seen from the ventral side. In the male 

 the ambulatory and abdominal feet of the left side ; in the female the ambulatory feet of 

 the right side and the maxillipeds of both sides have been removed. A anus ; A' anten- 

 nules ; A" antennae ; Doe opening of the green gland ; F', F" first and second abdominal 

 foot ; Goe genital opening ; M d mandible with palp ; MX', MX" first and second maxillae ; 

 Mxfi to Mxfi the first three pairs of maxillipeds ; Ov eggs ; PI scale of antenna. (After 

 Claus.) 



between the head and thorax. That this is the case appears very doubt- 

 ful from a consideration of Gnathophausia. In this Schizopod, the dorsal 

 shield extends back over the succeeding segments, but does not appar- 

 ently fuse with them, the eight thoracic terga remaining distinct.* The 

 shield appears to be in this case as clearly limited to the head region as 

 that of Apus or Nebalia. Towards the front of the upper surface of the 

 shield there is however a groove, which is identical in position with the 

 " cervical groove " of Astacus. In Gnathophausia therefore it appears that 

 the groove is very far from marking the posterior limit of the head. 

 It was named cervical groove by H. Milne-Edwards who regarded it as 



* Cf. Sars Challenger Report. Schizopoda, pi. 8, Fig. 17. 



z in LL 



