818 Proceedings of the Royal Irish Academy. 



1895 were identified as T. flavidum^ var. longissimum, Joubin. 

 Several more were obtained at Valencia in 1896, and I tave 

 since found the species not infrequently in Plymoutb Sound. I 

 think tbere is little doubt that Biirger is right in identify- 

 ing Joubin' s variety longissivium with his own new species 

 Nemertopsis tenuis ; and its removal from the Tetrastemmidse to 

 the family I^emertidse, with a new generic name, is certainly 

 justified by the relative shortness of its rhynchocoelom, which 

 is confined to the anterior half of the body (or less). In some 

 individuals the proboscis is not longer than one-foiu'th or fifth 

 of the total length of the animal. The relations of this form to 

 Tetrastemma flavidum will be discussed below. 



In form and colour Nemertopsis tenuis bears a strong 

 resemblance to Cephalothrix hiocidata, as pointed out by Joubin 

 and Biirger; in point of fact, small examples are indistinguish- 

 able to the naked eye. 



Distribution. — Plymouth Sound ; Falmouth Harbour 

 (W. I. B.) ; Brittany (Joubin) ; IS'aples (Biirger). 



Nemertopsis flavida (M'Intosh). 



Tetrastemma flavidum, M'Intosh (1874), p. 170; Riches (1893), 

 p. 13; Joubin (1894), p. 157; ?Burger (1895), p. 585. 



The E^emertine here referred to is not uncommon at Ply- 

 mouth and is considered by both Riches and myself to be the 

 Tetrastemma flavidum of M'Intosh. Since, however, the rhyn- 

 chocoelom does not usually extend back more than half the 

 length of the animal, never as much as two-thirds in my 

 experience, I have placed it in the genus Nemertopsis among 

 the Nemertidce. It is undoubtedly closely related to N. tenuis 

 (and consequently it is difficult to believe that it can be th& 

 same species as the Tetrastemma flavidum of Biirger), and, 

 indeed, I am still in doubt whether to regard the two as 

 varieties only, as does Joubin, or as distinct species. 



N. tenuis appears to me to be somewhat more slender, and in 

 particular to be more tapered towards either end than N. flavida, 

 which maintains a more even thickness throughout. The 

 difference, however, is slight, and may depend on the state of 

 extension of the animal. 



The rhynchocoelom appears to be relatively shorter in N. tenuis 

 than in N. flavida, being usually only about one-fourth of the 

 length of the body in the former, and nearly one -half in the 



