58 NILS HJ. ODHNER, STUDIES ON RECENT CHAMIDAE. 



The foot is elongated and very much compressed. Its length is nearly 4 times 

 its breadth and more than 1 / 4 of the length of the anterior adductor. 



The g i Ils cover about half the posterior part of the body, leaving the palps 

 free, because there is a sinuosity of the anterior gill margin. Both pairs of gills 

 have the upper margins of their reflected laminae completely free from the body 

 and their lovver ends separated from each other. 



Internal anatomy. 



The intestinal canal (fig. 71). The mouth is nnusually broad and very obli- 

 que, opening higher up on the left side than on the right, and the left palpi are 

 inserted much above the right ones. 



Al ready above or at the level of the entrance of the oesophagus into the 

 stomach there debouches on the left side of the latter, which is expanded trans- 

 versally so as to form a sharp corner on eaeh side, one large anterior finger-shaped 

 coecai appendage. Beneath and in front of it a short liver duct opens from behind 

 and immediately beneath the cardia a larger left canal with many branches, which 

 descends for some distance but soon disappears among the liver folliculi. On the 

 right side the liver ducts debouch at a lower level. A large median one receives 

 laterals from both left and right, and beneath it a still shorter left one appears. 

 At about this level there. emanates on the right side (in both specimens examined) 

 a posterior coecai appendage which projects some distance towards the intestine. 

 Beneath it follows the duodenum, with its narrower furrow situated on the right. 

 The intestine describes a coil behind the end of the duodenum, then widens some- 

 what in its middle part, pierces the heart and terminates in the usual way. 



The liver is asymmetrically developed: the left side is highly elevated and 

 produced into the left umbo, and the lower part descends somewhat deeper than 

 that of the right side which covers the stomach and the intestine laterally in their 

 upper parts and descends behind them farther down, while the left lobe of the liver 

 is retained only in front of the stomach. Being thus asymmetrically produced, the 

 liver shows in addition a slight torsion from the left towards the front and the right. 



The circulatory system. The anterior aorta forms a small sinus in front 

 of the pericard. From here there start as usual a dorsal and a ventral trunk. The 

 former passes upwards to the right of and above the stomach towards the front, 

 then descends above and to the left of the oesophagus. Immediately above the 

 mouth it divides into a branch which runs to the front of the mouth and from 

 there sends vessels to the anterior adductor, and a posterior vessel which passes 

 into the foot as arteria pedalis. A short lateral diverges from the root of this 

 dorsal trunk över to the liver and the genital folliculi into the right side of the body. 



The descending aorta trunk follows the left side of the intestine downwards 

 and passes över to the duodenum somewhat below the lower end of the coecai 

 appendage (on the level of the mouth). Having formed a large sinus it divides into 

 two branches, which embrace the duodenum and descend deeply down along its sides. 



