424 DISCOVERY REPORTS 



H. sinuosum (var. variabilis}) and H. leontodon forma cornuta. Braem suggested that 

 the presence of hyperstomial ovicells in Bugula apsteini might nevertheless make it 

 necessary to place it in a separate genus, but with my modification of the genus this 

 difficulty does not arise. 



I have examined the type-specimens of H. mirabile (87. 12.9. 182), H. margaritiferum 

 (87.12.9.200) and H. leontodon (87. 12.9. 177). In all of these, and particularly the 

 first two, the tentacles are very long and the other parts of the polypide are much 

 reduced as described by Braem. No caecum is discernible in a whole mount and the 

 pharynx is slender. 



In H. antarcticum and H. obtusum, on the other hand, the gut is well developed and 

 has a quite conspicuous caecum and a rotund pharynx. Braem described the pecu- 

 liarities of his species in comparison with Bugula neritina. I have compared spirit- 

 preserved specimens of Himantozoum antarcticum from St. 474 and of Bugula neritina 

 from the Suez Canal (26.9.6. 133 f). These were decalcified and mounted whole, the 

 Himantozoum being stained with borax carmine, the pigmentation of the Bugula sufficing 

 without staining. Fully grown polypides in similar positions were compared, and no 

 significant or constant difference in size, shape or proportion of parts was observed. 



In the type-specimen of H. sinuosum (87. 12.9. 179) the whole polypide is longer and 

 more slender than in H. antarcticum, the tentacles are relatively longer, and a caecum 

 is not discernible, but the rest of the alimentary canal is quite well developed. 

 H. sinuosum, which apparently ranges from 146 m. to 3397 m., is thus more or less 

 intermediate between the abyssal forms and the two relatively shallow-water species, 

 H. antarcticum and H. sinuosum. 



2. Himantozoum obtusum sp.n. Fig. 37 A, C. 



Station distribution. Sub- Antarctic : South Atlantic Ocean, Sts. WS 85, WS 93, WS 225, 

 WS 228, WS 229, WS 231, WS 246, WS 249, WS 783, WS 871. 



Geographical distribution. Patagonian Shelf (Discovery); off Patagonian Shelf down to 1098 m. 

 (Discovery; 34. 11. 12. 12 from Challenger St. 320). 



Holotype. St. WS 228, off Patagonian Shelf. 



Description. Colony usually bi- or triserial. Uniserial at base and occasionally 

 quadriserial before a bifurcation. Bifurcation as in other species of Himantozoum. 



Rootlets as in H. antarcticum. 



Zooecia like those of H. antarcticum except that they are smaller and are rounded 

 distally, without angles or spines (Fig. 37 A). "Tubulure" (of Calvet) present. 



Avicularia absent. 



Ovicells on median zooecia very shallow, without associated spines (Fig. 37 A, C). 

 Embryo develops in large sac in body cavity. 



Remarks. This species, which is confined to the Patagonian region, is very similar 

 to H. antarcticum. In addition to its more slender colony, and the differences already 

 noted in the zooecia and ovicells, there appears to be a slight difference in the shape 

 of the opercula, those of H. antarcticum being more angular, their shape correspond- 

 ing to the shape of the distal end of the zooecium. In H. obtusum the opercula of the 



