278 DISCOVERY REPORTS 



which is 0-074 mm - l° n g mounted on a pear-shaped base o-ioi mm. long. Branches of 

 the anterior caecum do not reach the brain. 



The brain is small. There is a dorsal strand in the lateral nerve. The cerebral organs 

 are fairly large. They open on the under-surface of the head but do not reach the brain. 



On two fronds of the red alga dredged with the large haul of this species a semi- 



Fig. 52. Tetrastemma validum, Burger. Graphic 

 reconstruction of the head to show the develop- 

 ment of the head glands and the position of the 

 brain, cerebral organs, eyes and branches of the 

 anterior caecum. 



Fig. 53. Tetrastemma validum, Burger. Mem- 

 branous pouch, open at both ends, attached to 

 a frond of red alga. 



translucent sheath was found attached. The length was 28 mm., breadth 5-0 mm. The 

 pouch was open at both ends and from one the animal crawled while under observation 



(Fig. 53)- 



In several characters this species is similar to Amphiporus michaelseni, Burger, as de- 

 scribed by Joubin (1908), but the four eyes and the internal structure show that its 

 affinities are with Tetrastemma. 



Tetrastemma weddelli, n.sp. (Figs. 54, 55). 



One specimen (N 70) was collected at St. 160 between South Georgia and the South 

 Orkney Islands. No note was made of the colour or form, but its anatomy is so dis- 

 tinctive that it should be easily recognized. The body was cylindrical, 11 mm. long 

 and 075 mm. broad. The proboscis was protruded to a length of 5-5 mm. and just be- 

 low it was the frilled opening of the mouth. The colour was bleached (Fig. 54 A). 



