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On the Occurrence of a Northern Hydroid Halatractus 

 (Corymorpha) nanus (Alder) at Plymouth. 



By 

 Dr. E. Stechow, Munchen. 



With Plate VII and Figure 1 iu the Text. 



On looking over some hydroid material, for which I have to thank the 

 Biological Station at Plymouth, I found upon an alga that was thickly 

 covered with Eiuicndrmm allnun, Nutting,* between the stalks of the 

 Eudendrium a single specimen of the rare Halatractus {Corymorpha) 

 nanus (Alder), which has until now been considered an Arctic species. 

 The specimen is of special interest owing to the fact that this 

 form has only been exceptionally met with in subarctic waters,, 

 and has only been recorded in England as a special rarity from 

 the colder coast of Northumberland [Hincks, 1868; Allman, 1872; 

 Pennington, 1885]. As far as can be gathered, it has only been 

 found once even there. Its discovery now at Plymouth, on the- 

 warm southern coast washed by the Gulf Stream, is therefore the 

 more surprising. In the comprehensive list of the Marine Fauna of 

 Plymouth in this Journal (N.S., Vol. VII, pp. 155-298, 1904) the species 

 is not included. 



Corymor'plui nana. Alder, Catalogue of Zoophytes of Northum- 

 berland and Durham. Trans. Tyneside Nat. Field Club,, 

 Vol. Ill, p. 108, PL 9, Figs. 7-8. 1858. 



Corymorpha nana. Hincks, A History of the British Hydroid 

 Zoophytes, p. 130, PI. 22, Fig. 3. 1868. 



Halatractus nanus. Allman, Monograph Tubularian Hydroids,. 

 p. 391. 1872. 



Corymorpha nana. Pennington, British Zoophytes, p. 78. 1885. 



Corymorpha nana. Bonnevie, Hydroida, Norske Nordhavs Ex- 

 pedition, p. 22, PL 1, Fig. 7. 1899. 



Corymorpha nana. Bedot, Materiaux, 2™^ periode. Eevue Suisse 

 de Zoologie. Tome 13, Fasc. 1, p. 63, 1905. 



Corymorpha nana. Broch, Hydroiden der arktischen Meere. Fauna 

 Arctica, Bd. 5, Lfg. 1, p. 194. 1909. 



Halatractus nanus. Bedot, Materiaux, 3"^^ periode. Eevue Suisse 

 de Zoologie. Tome 18, Fasc. 2, p. 304. 1910. 



* Jour. Mar. Biol. Assoc, N.S., lY, p. 146, 1896, and Ann. Mag. Nat. Hist., 7 seiv 

 Vol. I, p. 362, PI. 14, Fig. 1, 1898. 



