21 
The excretory duet opens somewhat cephalad to the base of 
the buccal cavity, 30 /i from the front end. There is a pear-shaped 
ampulla, the greater part of which is protoplasmatic. The chitinous 
excretory tube is rather long. The ven- 
tral giand is found a considerable dis¬ 
tance caudad to the base of the æso- 
phagus; in the larger of the two specimens, 
the length of which makes 3,9 mm, it is 
situated c. 170 fi caudad to it. 
The vulva is situated 2,8 mm from 
the front end, that is to say a consider¬ 
able distance caudad to the middle of 
* 
the body. The female organ is asymme- 
trical and found in the body-eavity ce¬ 
phalad to the vulva. In the uterus four 
shell-eggs are seen. The distal part of 
the ovary is reflexed. 
It is with some hesitation that I refer 
this species to the O. viridis of Bastian. . „ . 
With the insufficient material at my dis- 
posal and considering the somewhat compendious description of 
Bastian, I am not able to settie the question with certainty. 
Thoracostoma Marion. 
Excepting some questionable forms, the species belonging to 
this genus are well characterized and form a very natural group. 
Nevertheless it is possible among the hitherto described species to 
point out some species which are more closely related to one 
another than to the other species of the genus. I shall not enter 
more thoroughly on this question here, but only point at the two 
species described by de Man in the results of the Belgica-Ex- 
pedition, T. setosum v. Linst. and T. antaretieum v. Linst. These 
two forms are mutually closely related, and mueh doser related to 
each other than f. inst. to the forms from the Mediterranean de¬ 
scribed by Tiirck and by Marion. Perhaps it would prove to be 
justifiable to form a special group, possibly a subgenus for these 
two species, and to this group the European species T. figuratum 
Bastian, described by de Man, would also have to be referred. 
