BEYOZOA FROM ZANZIBAR. 527 



The furcate aviculai-ium at the pi-oximal end of the fenestra 

 is not so large or as much divided as in the 'Challenger' specimen, 

 but this divided avicularium is a character of much use in dis- 

 tinguishing the species from B. hirsuta B. and some others about 

 the same size with various zoarial characters similar. There are 

 no other large avicularia on the fenestral border, and there is a 

 delicate spine at each side of the oral aperture. As Miss Thornely 

 found in the specimen from the Indian Ocean, the growth some- 

 times brings the celluliferous surface to the outside as in 

 R. philijjpensis B. 



Ortmann has described a species as R. axillaris which has 

 an avicularium at the proximal end of the fenestra, but the 

 shape of the avicularium and mandibles differs from the species 

 from Zanzibar in which the avicularia are similar in shape to 

 those of R. Mrsida. 



There are 11 tentacles, and the oral glands are moderately 

 large but not much elongated. 



Log. Cape York, 8 fath. (5t(s^) ; Gulf of Manaar (TVi.) ; Caspar 

 Straits, Malacca Straits {Th.), var, Wasin, Brit. East Africa, 10 

 fath. (501), Ras Osowamembe, Zanzibar Channel, 10 fath. (501), 

 10-20 fath. (504, 514), collected by Crossland. 



?BiFAXARiA VAGANS Thornely. (PI. LXV. figs. 13, 14.) 



Thornely, "Mar. Polyzoa of the Indian Ocean," Trans. Linn. 

 Soc, Zool. vol. XV. p. 145, pi. viii. fig. 7 (1912). 



Zoarium erect, cylindrical, about 0'3 -0"4 mm. in diameter, 

 branches dividing dichotomously at nearly right -angles, continuous 

 in the younger portions, but in the older the junctions are broken 

 across and there is a chitinous tube inside the articulation. 

 Zooecia face opposite all round tlie stem in four directions ; the 

 surface of the zocecia has longitudinal ridges and large pits. The 

 secondary orifice is round with a small mucro bearing a small 

 avicularium, with an acute triangular mandible extending into 

 it, while the primary orifice, which is some distance down the 

 peristome, has the proximal edge straight. There are no ovicells 

 on the specimens examined, which were growing on Retepora, 

 nor were any ovaria or testes found in the sections made. There 

 does not appear to be any bar to the avicularium. There are 

 about 16 tentacles. 



This is much like the ' Challenger' Bifaxaria reticulata* Busk, 

 but in the British Museum specimens there are no avicularia, 

 and the surface is reticulate and apparently not perforate. 



Bifaxaria of the ' Challenger ' is not a satisfactory genus, and 

 will be broken up. It might be retained for B. submucronata B. 

 and B. corrugata B., which are closely allied, and have the 

 avicularia at the proximal end of the zooecia, not at the distal 

 end as supposed by Busk. B. denticulata B. has been removed 



* Busk, Zool. Cliall. Exp. vol. x. pt. xxx. p. 82 (188i). 



