KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 43 



External morphology (fig. 46). 



Mantle. Its edge as well as that of the siphonal openings is completely smooth, 

 the former only somewhat wrinkled. The siphonal openings together occupy less 

 than half the distan ce between the adductors; the pedal slit is very small and 

 situated immediately beneath the end of the anterior adductor, in front of which 

 the lobes of the mantle are entirely separated. Under the expiratory opening a 

 comparatively narrow siphonal tube projects between the ends of the gills. The 

 right umbonal process is formed exclusively by the thickened mantle and contains 

 no viscera. From the umbo a stripe of this thickening runs downwards in the 

 bottom of the cavity formed by the upward deflection of the posterior part of the 

 lower valve. 



The anterior adductor is decidedly shorter than the distance between the 

 upper ends of the adductors and about twice as long as the posterior muscle. 



The labial palps are situated at different heights, those on the left side 

 being attached at the upper end of the anterior adductor and attaining about Vio 

 of its length ; those on the right side being inserted higher up and remote from the 

 adductor and having their tips turned backwards. Both pairs are connected by 

 lips and striated on their adoral surfaces. 



The foot is falciform, somewhat diiated distally, compressed, its length a little 

 less than twice its breadth and about a fifth of the length of the anterior adductor; 

 the body behind the foot is convexly rounded, with a small triangulär lobe at a 

 distance from the foot equal to the length of the same. 



The ends of the gills häng freely and have the upper (posterior) margins of 

 their reflected plates separated from the mantle and the body; the ends of the gills 

 are also free from each other, but loosely cover a siphonal fold which projects be- 

 tween them. At the mouth the anterior margin of the anterior gills partly covers 

 the posterior labial palps, there being only a slight sinuosity above the mouth. The 

 remaining part of the visceral hump, except the end of the foot, is also covered by 

 the gills, which are produced farther upwards on the right side. 



Internal anatomy. 



The intestinal canal (fig. 47). The oesophagus shows in transverse section 

 one dorsal list and one ventral furrow as well as 4 lateral furrows on each side. 

 Before its termination into the stomach it describes a dorsal curve. 



The stomach has also a convex dorsal outline and is furnished with a short 

 coecal appendage. Into the stomach debouch : the principal liver canal in front of 

 the left side, originating from the liver folliculi of the left side, and farther above 

 some small canals on the right side. Into the coecal appendage and on its sides 

 rather small liver canals also terminate. 



