432 " THETIS " SCIENTIFIC RESULTS. 



, Of the pallial complex it is sufficient to say that the 0S2)hradiu7n, 

 ctenidium, rectum, and uterus differ from those organs in M. 

 aruanus only in being proportionately smaller. 



The hypohranchial mucous gland is more than proportionately 

 reduced ; it presents none of the complex arrangement of ridges 

 in this species which it does in the last. 



The ureter is absent. 



The position of the vas-deferens and penis will be described in 

 connection with the reproductive organs. 



2. Digestive System. 

 (PI. xxxix., fig. 6.) 



The orifice of the pi^oboscis sheath (pr. sh. ) is situated, as in the 

 last species, close down to the front margin of the foot, and is 

 overhung by the tentacle lobe and tentacles. The sheath itself 

 is not so intimately fused with the dorsal body wall as in 31. 

 aruaiius ; on the contrary, it is a self-contained portion of the 

 proboscis, and though attached to the body wall by numerous 

 strands of muscle and connective tissue, may be dissected out, 

 only a few millimetres of the anterior end being completely fused 

 with the wall, nevertheless, it is not evaginable. 



The proboscis sac. {ph. sac.) is longer and smaller in diameter 

 than in the last species, but is otherwise essentially similar. 



The proboscis is longer in this species than in the last. 



The mouth, buccal mass and oesophagus within the proboscis, 

 are all essentiall}'' similar to what was found in M. arttanus. 



The radula (Pi. xl., fig. 4) is of the same length and dental 

 formula (1, 1, 1) as in the last species, but the individual teeth 

 are somewhat different. The rachidian is tricuspid, cusps nearly 

 equal sized, the central slightly the largest, the lateral cusps 

 attached much nearer the margin of the base than in M. aruanus; 

 base of attachment half as deep as broad. Laterals tricuspid, 

 base of attachment not deep ; the outer cusp the largest, placed 

 at the extreme outer margin of the base, the other two cusps 

 equal in size, attached near the inner margin. 



The oesophagus issues from the proboscis at the posterior end 

 of the sac, and passes forward attached to the left side thereof 

 (ant. ces ). At the anterior end of the sac it bends down and 

 comes to lie on the floor of the body cavity. It here becomes 

 suddenly swollen, and then slightly narrowed again, but is thence 

 for the rest of its length a larger tube than that portion which 

 lies between the swelling and the buccal cavity. These two 

 portions may be distinguished as the " anterior" and "posterior" 

 oesophagi. The posterior oesophagus (post, ass.) continues forward 

 to the anterior end of the body cavity, where lie the main ganglia, 



