HYDROID ZOOPHYTES. 29 



annulated and very irregularly branched. They are not more than O'l mm. in 

 diameter. 



The hydrothecse are elongated and everted at the margins. They are 

 frequently reduplicated. 



The hydranths are 0-5 mm. in length and have about 20 tentacles 0-25 mm. 

 in length. There are no nematophores in this species. 



Gonosome. — The gonothecse are oval (O'S x 0'5 mm.) or spherical in both 

 sexes. They are situated on short pedicels which may be irregularly anuulated as 

 in the British type. They are situated on the hydrocauli in no definite position. 

 There is no evidence of any " coppinia "-like grouping of the gonothecse. 



The species Halecium tenellum was obtained by the ' Belgica ' expedition in 

 70° S. by 91° W., and Bale mentions that he has one specimen in his collection 

 from the Australian waters. It has also been found on the south Fuegian coasts 

 and in Smyth Sound (10 : pp. 505-509). It is common on the British and 

 American coasts and extends into the Arctic seas (Jan Mayen). In fact, it appears 

 to be cosmopolitan in Arctic and Temperate seas. 



SUB-FAMILY LAFOEINAE. 

 Lafoeina longitheca. 

 (Plate IV., fig. 31.) 

 Lafoeina longitheca, Jaderholm, Arch. Zool. Exp6r. (4), III. (1904), p. iv. 



XomZ%.— McMurdo Bay, February 20th, 1902 ; 5-20 fms. 



Two small colonies of this hydroid were found creeping on the free hydrorhiza 

 of Perigonimus antarcticus. 



Hydroso'ine. — A well-developed hydrorhizal filament is attached to the support. 

 From this there arise at intervals tall, cylindrical hydrothecse (fig. 31) 0*7-l"0 mm. 

 in height, slightly annulated at the base, and gracefully everted at the margin. 

 The margin bears about twelve opercular flaps (fig. 31, op.), 0*11 mm. in length. 

 Occasionally secondary hydrothecse arise from the primary ones and attain an 

 additional length of 0*25 mm. There is no distinct pedicel, the diameter of 

 the hydrotheca at the base being almost as great as it is at the distal extremity. 



The hydranths are very small, being in the contracted condition not more than 

 0*4 mm. in length, or about half that of the hydrotheca. A circlet of about eight 

 tentacles surrounds the blunt conical hypostome. Each tentacle is about 0"13 mm. 

 in length. 



Numerous upright nematophores, 0'12 mm. (but occasionally 0*2 mm.) in height 

 by 0-02 mm. in diameter, arise independently from the hydrorhiza. They contain a 

 delicate thread of tissue (fig. 31, cL), terminating in a pad at the extremity which 

 is armed with a battery of nematocysts. 



Gonosome. — Not observed. 



