KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 45 



Pseudochama cristella Lamarck. 



Figs. 50-53. 



Some specimens from the north-western coast of Australia, collected by Dr. 

 Mj Öberg (ef. Odhner 1917) have been studied. 



External nioiphology (fig. 50). 



The mantle is thin, only slightly thickened on the ridge of the right side and 

 in the right umbo, which forms a cornet. Its margins are minutely papillated; the 

 inspiratory siphon is rather small, smooth-edged, and the anal orifice has a large 

 siphonal fold; both orifices occupy somewhat less than a third of the whole under 

 margin. The pedal slit lies beneath the anterior adduetor and is a little shorter 

 than half its length. 



The adduetor muscles are unequal in size, the anterior one about lj times 

 the size of the postenor one and removed from it as far as its own length. 



The labial palps are short, not exceeding l J& of the anterior adduetor; the 

 right ones are attached higher up. 



The foot is rather small, not exceeding the length of the palpi; compressed 

 laterally and somewhat dilated towards the end; behind it the visceral hump hängs 

 as a pouch (in mature specimens) and a minute triangulär lobe is present far back. 



The gills cover the whole body; the anterior one is not twice as broad as the 

 posterior. The ones on the right side extend farther upwards than those of the 

 left side. The mode of attachment of the gills varies. A full-grown specimen has 

 them hanging freely behind, thus separate from each other and from the mantle; 

 the reflected laminae of both gills are free from body. In two smaller specimens 

 the gills are united to each other behind; in one of them they are, in addition, 

 attached by their tips to the mantle. 



Internal anatoiuy. 



The intestinal canal (fig. 51). A wide primary liver canal branches off to 

 the left side of the body immediately beneath the end of the oesophagus, and a 

 narrower one debouches on the right side, as well as a great many smaller ones 

 everywhere in the stomach. A very short descending coecal appendage is differ- 

 entiated on the right of the median line. The duodenal part is split into the two 

 longitudinal furrows as usual, the narrower one situated on the right and the broader 

 one on the left. By means of a single flexure the duodenum passes into the 

 intestine. 



