REPORT ON THE NEMERTEA. 25 



when put into salt water would live there for twenty-four hours, but when put into fresh 

 water died after a few hours time. Fresh water, however, poured over the earth which 

 contained them, did not damage them in the least." 



Tetrastemma fuscum, Willemoes Suhra {nee (Ersted). 



A second species of Tetrastemma was noticed by Suhm during the first year of the 

 Challenger cruise. In the paper just referred to, in which he describes Tetrastemma 

 agricola, it is noticed in the following words: — 



" I may here also add that on our cruise from the Bermudas to the Azores I found 

 parasitical Nemerteans on Nautilograpsus minutus, one of the gulf-weed crabs. They 

 were small brownish animals, and occupied especially the underside of the crab, under 

 the abdomen of which I found most of them. They did not exceed the length of 2 mm. 

 and in none of them could I see genital organs. In fig. 4 I have figured one of these 

 small parasites, which probably also belong to the genus Tetrastemma, though the second 

 pair of eyes is only punctiform, situated on both sides of the proboscis. Nervous system 

 and digestive apparatus do not present anything particular, and the proboscis 

 (fig. 4, pr\ pr'), is remarkable for its shortness. 



" I do not think that these worms attain their full size on the crab, but believe them to 

 be young parasitical stages of some Nemertean which possibly lives on the gidf-weed." 



In his journal, of which an abstract is given in the Narrative of the Cruise, vol. i. 

 p. 169, Suhm further remarks about this species : — • 



" The worm presents no modification induced by jiarasitism ; it appears to be a new 

 species, and from its colour may lie called Tetrastemma fuscum. . . . The ganglia are 

 especially large and conspicuous. . . . The proboscis is very short, and distinguished 

 from all other species I know of by having the stylet-sac placed close behind the ganglion 

 and just above the mouth. . . . Length 075 mm., breadth 0"25 mm." 



Suhm was apparently not aware that the specific name which he gives to his specimen 

 was preoccupied for another Tetrastemma, as early as 1844, by Glrsted for the species 

 that is now known as Tetrastemma dorsalis. 



No specimen being jDreserved, the special features enumerated by Suhm do not justify 

 me in proposing a new specific name. For completeness' sake it was, however, necessary 

 to mention his observations. 



Family P E L A G O N E M E E T l D .^. 



Pelagonemertes, Moseley. 



Pelagonemertes rollestoni, Moseley. 



It was indeed a novel and startling fact when detailed news ^ appeared regarding the 

 capture by the Challenger naturalists of a pelagic Nemertean, which, in addition to other 



' Ami. and Mag. Nat. Hist., ser. 4, vol. xv. p. 165, 1875 ; vol. xvi. p. 377. 

 (ZOOL. CHALL. EXP. — PART Liv. — 1886.) Hhli 4 



