THE CEPHALOTHOBAX. 151 



pleurobranchia (fig. 4, plb. 14) is attached; and in 

 front of this, it is connected, by a narrow neck, with 

 an elongated triangular piece, which takes a vertical 

 direction, and lies in the fold which separates the posterior 

 thoracic somite from the next in front. The base of this 



t, xv. 



FIG. 38. — Astacm flvviatilis.— The mode of connexion between the last 

 thoracic and the first abdominal somites ( x 3). a, L-shaped bar ; 

 ejpe, carapace ; cxp. 14, coxopodite of the last ambulatory leg ; plb., 

 place of attachment of the pleurobranchia ; st. XV, sternum, and 

 t. XV, tergum of the first abdominal somite. 



piece unites with the epimeron of the penultimate somite. 

 Its apex is connected with the anterior end of the horizontal 

 arm of an L-shaped calcified bar (fig. 38, a), the upper end 

 of the vertical arm of which is firmly, but moveably, con- 

 nected with the anterior and lateral edge of the tergum 

 of the first abdominal somite if. XV.). The tendon of one 



