54 NILS HJ. ODHNER, STUDIES ON RECENT CHAMIDAE. 



duct follows on the left side. The latter receives branches from both right and left 

 liver folliculi and disappears at about the level of the mouth. The stomach has a 

 short median coecal appendage on its back vvall and a finger-shaped process pro- 

 jecting from the left side towards the front. The duodenum has a regular circular 

 section with the narrower furrow to the right throughout its whole length. Below, 

 the duodenum passes into the intestine by means of a simple flexure. Its median 

 portion is thickened as to form a colon. 



The circulatory system. The heart has well separated auricles. The anterior 

 aorta, as usual, is divided into a dorsal and a ventral trunk. The former gives off 

 a vessel into the mantle and runs forward to the left of the stomach and down- 

 ward along the left side of the oesophagus. Near the junction of the large liver 

 canal with the stomach, the aorta sends a small branch över to the under side of 

 the oesophagus; here it descends between this and the liver duct. In another spe- 

 cimen it gave rise to a vessel that encircled the duodenum. The chief trunk of the 

 present arteria penetrates to the vicinity of the mouth, where on the left side of 

 the oesophagus it gives off a branch towards the front. Somewhat beneath the 

 cerebral commissure it forms a transversal sinus, from which the anterior adductor 

 receives its arteriae. On the back side of the mouth the primary trunk descends 

 as arteria pedalis. 



The ventral branch of the anterior aorta is divided into a right and a left 

 vessel; both penetrate -downwards through the liver and the genital folliculi. In the 

 other specimen both soon disappeared, the right one first. The left branch in the 

 latter specimen reached the left side of the stomach and here detached a small ca- 

 pillary to the right; then it followed the left side for a short distance downwards 

 till it disappeared above the point where the coecal sac emerges. In the other spe- 

 cimen the course of the arteria gastrica was the normal. 



Thus the present species, in contrast with the other Chamas, exhibited the 

 peculiarity that in one specimen the arteria gastrica was much reduced and that its 

 function had been taken över by the gastral branch of the oesophageal arteria. 

 This arrangement, which was probably an occasional aberration, is the normal one 

 for most of the Lamellibranchia. 



The nervous system. In the cerebral complex there exist buccal ganglia 

 situated, as is usual in the genus, between the bases of the labial palps, and con- 

 nected by means of short cords to the cerebral ganglia. The cerebro-visceral con- 

 nectives pass inside the genital coeca, but do nöt penetrate the liver, and proceed 

 midway between stomach and body wall on the right side and somewhat nearer to 

 the stomach on the left; there is also a median commissure in front of the pericard. 



The nephridia are of the same type as in Ch. jukesi, with comparatively 

 short and narrow pericardial tubes, separated from each other by a lobe hanging 

 from the outer sacs. Only just behind the communication between the latter the 

 pericardial tubes immediately touch each other. Both nephridia are about equal in 

 size, but the left one is produced somewhat higher, namely above the rectum. The 

 ciliated funnels are rather long and the ampullae have the same shape and construc- 



