12 G. O. Sars. 



cephalic shield obliquely backwards between the anterior 

 part of the intestinal tube and the optic ganglion, the lab- 

 rum can be protracted to some extent, its retraction being 

 effected by 2 or 3 short muscles extending across its body. 

 Within the latter some cellular bodies are observed, ap- 

 parently of a glandular nature. 



No trace of any distinctly defined posterior lip is to be 

 detected. 



The mandibles are easily observable in the lateral view 

 of the animal (see PI. I, fig. 1; PI. II, fig. 1), originating 

 with their upper acute extremity just at the point where the 

 fornix joins the carapace, and extending downwards to the 

 mouth, their lower extremity being somewhat incurved. They 

 are not completely covered at the sides by the valves, a 

 part of their bodies being exposed in front of the anterior 

 edge (see PI. II, fig. 1). When isolated (fig. 3), they are 

 each found to consist of a hollowed navicular body, and a 

 more highly chitinized masticatory part defined from the 

 former by a slight neck-shaped constriction. The latter part is 

 transversely truncated at the end, and exhibits a finely fluted 

 triturating surface, outside which is a group of slender 

 teeth projecting somewhat beyond this surface. The mus- 

 cular apparatus of the mandibles consists of the adductor 

 and rotatory muscles. The former are very strong, filling- up 

 the hollow of the navicular parts, and are connected in the 

 middle by a chitinous tendon traversing the body below the 

 intestinal tube. The rotatory muscles are two on each side, 

 originating in the region of the cervical depression, and ex- 

 tending straight downwards, where they join the anterior 

 and posterior margins of each mandible (see PL II, fig. 1). 



The raaxillæ (fig. 4) are rather small, each exhibiting- a 

 thick basal part, to the end of which is attached a very 



