PLYMOUTH NEMERTEANS. 425 



infected with them. In ISTew England they live on Platyonychus 

 occllatus. 



Geographical distribution : 0. carcinophila has not been found 

 previously in England ; it has been recorded from the Atlantic coasts 

 of Belgium and France, from the Mediterranean and from New 

 England. 



Genus Nemertopsis. 



As Fniplccionema, but instead of many, only four eyes, situated in a 

 rectangle. The distance between the eyes of one pair is smaller than 

 that between the eyes of one side. 



1. Nemertopsis flavida (Mcintosh), Beaumont. (Mcintosh. Monogr. 

 PI. IV, Fig. 1 ; and Joubin, Les Nemertiens, PI. II, Fig. 61.) 



Locality : Common in the Sound, both from dredgings and between 

 tidemarks. Once from a dredging near the Mewstone. 



Under this name I unite both the Nemertopsis species, described by 

 Beaumont (1900, p. 817 and 818). It seems to me very doubtful 

 whether N. tenuis must be distinguished from N. Jiavida. The only 

 difference between the two so-called species is to be found in the 

 colour, which is quite white in N. jiavida and a very faint pink in 

 iV. tenuis. This, however, might be due to the colour of the blood, 

 which is decidedly red in the last species and cannot be seen in the 

 first. Moreover, the colour of Tetrastemma flavida, Mcintosh, is pinkish 

 or pale peach, which agrees with Nemertopsis tenuis, not with N. flavida. 

 Beaumont states a difference in the extension of the proboscis sheath. 

 This I have not been able to ascertain. A difference in body length of 

 the animals might have caused this just as well, especially as the 

 worms very easily break into pieces. No other difference between 

 N. flcivida- and tenuis has been described. As to the value of the red- 

 blood colour, this is not a character on which alone to base a new 

 species. As long as no other difference between these two forms is 

 known, we cannot regard them as separate species. Perhaps they are 

 only varieties of one species, but even this seems questionable 

 to me. 



Moreover, Beaumont does not seem to be quite certain himself as to 

 the value of his distinction. "The doubtful status of Nemertopsis tenuis 

 as a species distinct from N. flavida, Sind the fact that they have rarely 

 been distinguished with certainty, make it expedient to consider them 

 together (W. I. B.)." (Plymouth Marine Invertebrate Fauna, 1904. 

 Nemertea.) 



In this case the name Nemertopsis temois, Bilrfjer, has to be dropped ; 

 it must be replaced by Nemertopsis flavida {Mcintosh), Beaumont, which 



KEW SERIES.— VOL. IX. NO. 3. JUNE, 1912, 2 E 



