244 



DISCOVERY REPORTS 



muscles. Glandular tissue encloses the canals and a nerve from each dorsal ganglion 

 passes into the organ. 



The dorsal ganglia are smaller than the ventral. There are ten nerves in the proboscis. 



No excretory vessels or ducts could be traced. 



The armature consists of a main stylet on a base somewhat longer than itself and two 

 accessory reservoirs. In one worm three accessory stylets were present in each reservoir 

 but in others there were only two. The lengths were as follows: 



Main stylet 0-067 mm -> accessory stylet 0-058 mm., base 0-077 mm - 



This species appears to correspond with Tetrastemma incisum, Stimpson (1856). 

 I can see no reason for separating it from T. candidum, Muller, since in size and shape 

 of the body and head, and in the absence of markings it agrees closely with a colour 

 variant of this species. 



Tetrastemma nigrolineatum, n.sp. (Plate XV, fig. 9; Fig. 17). 



A single specimen was taken in July from a kelp root inside the Bay. The length was 

 25 mm., breadth about 0-3 mm. 



This slender worm appears to be rectangular in section, and the head is wedge-shaped 

 when seen from the side. There are no eyespots and neither mouth nor cephalic slits 

 are visible. The colour is whitish green, with two parallel 

 black lines passing down the back from tip of snout to tip 

 of tail. At the head these lines are thinner than they are 

 on the body. 



In spirit traces of the double dark line can be seen. 



Internal structure. Head glands are absent. The epi- 

 thelium is about as thick as the longitudinal muscle layer. 

 The basement membrane and circular muscles are thin. 

 The former is thinner than the latter and stains with 

 haematoxylin. Brown pigment granules are present at the 

 base of the epithelial cells where the dark lines can be 

 seen in life. There are no traces of eyespots. 



The oesophagus opens into the rhynchodaeum, and 

 the common pore is ventral to the tip of the head. The 

 narrow oesophagus opens into a folded stomach with 

 deeply staining walls just posterior to the dorsal ganglia. 

 The unbranched anterior caecum ends a long way behind 

 the brain. 



The proboscis extends well into the posterior half of 

 the body, and the rhynchocoel into the posterior third. 

 The armature consists of a single main stylet on a reddish 

 brown base and two reservoirs with seven or eight accessory stylets. Some of these 

 are incomplete. 



Fig. 17. Tetrastemma nigro- 

 lineatum, n.sp. Diagram from a 

 graphic reconstruction of the 

 brain, cerebral organs, excretory 

 and alimentary systems. 



