KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 47 



6. Anatoinical researches 011 species of Chama. 



Chama reflexa Broderip. 



Figs. 54, 55. 



The following facts are based on a few specimens from the north-western coast 

 of Australia collected by Dr. Mj Öberg and referred by me to the typical form of 

 this species (ef. Odhner 1917). 



External niorphology (fig. 54). 



Mänt le. This is thin all över the body, only slightly thickened towards the 

 umbones, especially on the left side, where the umbonal region is a little more pro- 

 minent. In the lower margin the inner folds of the mantle have, as usual, coalesced, 

 leaving open a pedal slit vvith a length of from ' « to about half that of the an- 

 terior adduetor and ascending to about half its height before the mantle margins 

 join again. The two siphonal apertures together occupy nearly half (but less than 

 a third of) the under margin. The siphons are very short and have a single wreath 

 of small papillae round their base. They are usually pigmented, as is also the 

 interjacent rough area, but in specimens in which the shell is less coloured, the 

 pigmentation of this part lessens or is even entirely absent. The remaining part of 

 the fold of the mantle as well as the pedal aperture is smooth and uncoloured. 

 A siphonal fold projects beneath the exhalent aperture. 



The adduetor mu seles are about equal in length, or else the anterior one 

 is somewhat larger, and situated a distance equal to its own length from the post- 

 erior one. 



The labial palps are rather lengthened. The left ones are inserted higher 

 up than the right ones and are directed somewhat backwards. With their tips they 

 more of less reach beneath the upper end of the adduetor. The right ones are 

 inserted lower down (at the level of the uppér end of the adduetor) and are equal 

 in length to l /i or about ! the adduetor. They have about 15 longitudinal lists on 

 their adoral sides. 



The foot is compressed, short and broad (its length not more than twice its 

 breadth), tapering to a point and situated about twice its length from the mouth. 

 The visceral pouch terminates somewhat more than its own length beneath it, and 

 a large triangulär lobe is present above its end. This lobe attains a size equal to 

 that of the foot. 



The gills. The right pair are somewhat broader than the left ones and cover 

 almost the whole body, leaving only its frontal margin with the foot and the labial 

 palps free. The posterior gill has a well developed descending lamina somewhat 

 more than half the breadth of this demi-branch and about half as broad as the 



