THE ANATOMY OF MKfJALATliACTUS — KKSTEVEN. 423 



The opercu/uni is of the fusoid type (PI. xl., fig. 1), mytiloid 

 in shape, the nucleus liein,^ anterior. There is a slight ridge 

 along the right side, this ridge being more pronounced at the 

 posterior end than at the nucleus. 



The sole of the foot is of a light l)urnt umber ; the sides also have 

 this colour for a base, l)ut are so tlecked and splashed with black 

 as to appear in places quite black. The front margin of the foot 

 bears a groove for the conduction of mucous (?). 



There is no snout, and the tentacle lobe (tent, lb.), which 

 overhangs the orifice of the proboscis sheath is placed far forward, 

 so that that orifice is almost down on the front margin of the 

 foot. 



The tentacles (tent.) are short and thick, and bear the eyes on 

 prominences about a quarter of their length from the end. It 

 would better describe these organs to say that just beyond the 

 position of the eyes they become suddenl}' thinner. 



The dorsal region of the body and the surface of the mantle 

 are of a yellow colour. 



The mantle along its anterior edge, along the sides, and the 

 siphonal fold, is thick and tough ; over the body it is thin. The 

 siphonal fold (s.) is rather long, and can apparently be protruded 

 for some length. 



The columellar imiscle is long, though not very thick ; it is of a 

 yellow colour, and extends up the columella for a little more than 

 a whorl and a half ; the visceral coil is attached to it for as far 

 back as the posterior end of the pericardium. 



b. — Pallial Complex. 

 (PI. xli., fig. 2.) 



The lyallial cavity extends back to the posterior end of the 

 body, and is there bounded by the nephridium as usual. To the 

 usual number of organs in the pallial cavity there is added a 

 ureter. 



The ospliradiuni (osph.) is oval, tapering at both ends, but 

 rather more gradually posteriorly than anteriorly. It is dark 

 green in colour, and of a large size, therefore a prominent organ. 

 The lamelkie are broader distally than at the point of attachment 

 to the centre cord. 



The ctenidium (cten.) is curved-lanceolate in shape, tapering 

 more gradually posteriorly than anteriorly. It is a dull flesh- 

 pink colour, and extends from well forward in the cavity, on a 

 level with the anterior end of the osphradium, almost to the 

 posterior end of the cavity. Its lamellae reach their maximum 

 breadth a little distance from their free ends. 



The hyp>obranchial rnucous gland (tn.g.) is very large ; of the 

 same shape as the ctenidium, it occupies an area as large on the 



