THE SYNC A RID A 



163 



somite appears to be marked by a transverse " cervical groove " (c.gr} 

 which crosses the dorsal surface and runs obliquely forwards on 

 each side to end just behind the mandible. In Koonunga (Fig. 95) 

 this groove is obliterated dorsally, but a short portion persists on 

 each side running upwards from the lower margin of the head. 



C.gr 



FIG. 94. 



Annspi'lt:* tiixiiiiiuine, <$ , x 3. c.gr, "cervical groove " ; II, VIII, second and eighth thoracic 

 somites ; 1, 6, first and sixth abdominal somites. (Drawn by Miss G. M. Woodward.) 



It has been suggested that this groove indicates the limit between 

 the mandibular and maxillular somites and corresponds to the 

 " cervical sulcus " of the Mysidacea, and perhaps to the transverse 

 groove of the head in many Branchiopoda. On the other hand, 

 a forward displacement of the lateral plates of the anterior thoracic 



Fio. 95. 



Koonunga cvrsor, <J, x 11. (From an original drawing by 

 Mr. O. A. Sayce, slightly modified.) 



somites is observed in some other Malacostraca, and it is quite 

 probable that this groove in Anaspides has undergone a similar 

 displacement and that it really does define the first thoracic somite 

 from the head. Running backwards from this groove on eacu side in 

 Anaspides is a horizontal line marking off inferiorly a quadrilateral area. 



