KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 63. NIO 2- 25 



edged and rather broad. The dorsal tubercle is rounded and small, though pro- 

 minent. The aperture is elongate and feebly curved (Pl. 1, fig. 17). 



The branchial sac is provided with four folds on each side; three are well 

 developed, and one — the second — is in a rudimentary state. It is represented by 

 three longitudinal vessels, a number which is reduced to two in the bottom of the 

 branchial sac. On the interspaces between the folds there is one wide longitudinal 

 vessel. The following scheme shows the approximate number and the distribution of 

 the vessels: 



Dorsal lamina, 1(9) 1(3) 1(7) 1(5) 1, endostyle. 



The stigmata are elongated and of the usual form. 



The alimentary canal is not of great length. The stomach is short and has 

 a horizontal position. Numerous longitudinal plications are visible in its wall. No 

 pyloric coecum has been observed. The intestine forms a short loop and afterwards 

 bends upwards almost at right angles (Pl. 1, fig. 16). As appears from the figure, 

 the rectum is short and distinctly marked off from the intestine, from which it rises 

 at right angles. The margin of the anus is provided with seven small lobes. 



Te reproductive organs consist of one hermaphrodite gonad on each side of 

 the body. The gonad is of great length and characteristically bent into the shape 

 of the letter U (Pl. 1, fig. 15). In this individual it is well distended with eggs at 

 different stages of development. Macroscopically no male glands could be observed, 

 but from sections it appears that the gonad contains verv small glands — in all 

 probability, male glands, though no spermatozoa were observed there, — with ducts, 

 hidden by the mäss of large eggs. So far as one can judge from this single specimen, 

 the eggs and the spermatozoa are thus produced at different times. The ovary and 

 testis each open at the end of the gonad by an elongated duct dorsally directed. 

 Owing to the t/-shaped form of the gonad, its distal end with the opening ducts 

 almost touches its proximal end. The main sperm-duct lies upon the inner free surface 

 of the gonad, and ends at some distance from the oviduct. Macroscopically the väsa 

 efferentia were scarcely visible. 



Endocarps are present on the inner side of the mantle and in the loop of 

 the intestine. 



Remarks. 



In discussing the S3 7 stematic position of Ypsilocarpa the characters of the gonads 

 and the atrial tentacles should above all be considered. As far as one can judge 

 from this single specimen it agrees with the genus Cnemidocarpa as regards the 

 general structure of the reproductive organs, the ovan^ and testis not being separated. 

 In other respects, even as to the reproductive organs, it differs from that genus. 

 Cnemidocarpa has from few to many gonads, which are usually straight or tortuous. 

 Ypsilocarpa has, on each side, one gonad only, which is of considerable length and 

 bent in the shape of the letter U. 



In Cnemidocarpa the atrial tentacles are arranged in a single row at the base 

 of the velum. In Ypsilocarpa they are scattered över the velum. In Y. clipeata 



K. Sv. Vet. Akad. Handl. Band 63. N:o 2. 4 



