KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. NIO 3- 27 



running in a dorso-ventral direction; no such features are present in the left gill. 

 This flexure of the posterior part of the gill mentioned is due to the mode of 

 attachment by the right val ve. 



The posterior margin of this appendix is free from the body up to about half 

 the height of the nephridium; at this point it becomes fixed to the wall of the body. 

 The anterior edge of the outer gill shows no marginal furrow such as occurs in the 

 inner or foremost gill. In the posterior gill the same connections of filaments and 

 lamellae are developed as in the anterior one. 



The mode of junction to the body of the sheet margins is possibly subject to 

 variation; this is, however, impossible to decide because of the scarcity of material 

 at our disposal; in all the three specimens examined the conditions were completely 

 similar to each other and agreed with the above description. 



The microscopical structure of the gills is like that of Echinochama arcinella 

 (described below) with the exception that no inter-marginal connections between the 

 marginal and the axial vein exist in the anterior gill. 



The exteriör openings of the genital ducts are situated on the back wall of 

 the body close in front of and beneath the pericard, somewhat higher up than, but 

 separated from and opposite to the nephroprocts. The wall of the body here forms 

 a small pad outside and close below the ends of the ducts. 



Internal anatoniy. 



The intestinal system (fig. 24). At the sides of the mouth, as usual, two 

 pairs of oral palps are present. They are attached at the upper end of the anterior 

 adductor, both pairs at the same height and on both sides they attain about a third, 

 or somewhat less, but not half the length, of the adductor. On account of the 

 broadness of the body they are far removed laterally, and the mouth forms a narrow 

 fissure, bounded on its front and back sides by a thickened lip extending between 

 the bases of the opposite palps. On their adoral sides, which are turned outwardly, 

 the palps are furnished with close longitudinal lists, about 3 — 5 in number, each 

 accompanied with a secondary one as in Chama pellucida (ef. Grieser 1913); the 

 aboral sides of the palps are smooth. The hind palp is covered by the gill, but the 

 front one is left free. 



A short oesophagus leads to the stomach. It is orbicular in a transversal 

 section and contains the same number of lists and furrows as in Ch. pellucida. The 

 stomach . widens upwards and narrows posteriorly to a short coecal appendix. The 

 posterior wall of the stomach is lined with a high cylindrical endothelium with a 

 strong cuticula; towards the sides the endothelium becomes lower and the back wall 

 is bounded by a pair of deep pockets or furrows, limited on their front side by 

 strong limbs projecting inward. Just in front of these limbs debouch a pair of liver 

 ducts, the left one somewhat higher up than the right. Some rather large ducts 

 open in the före part of the stomach, on its sides; the sinistral one debouches some- 

 what lower and is the largest. It has a strong descending trunk of about the same 



