REPORT ON THE POLYZOA. 21 



uncommon in Retepora, and occur well marked in Retcpora imperati, also in Retepora 

 lata, Retepora cellulosa, &c., and probably depend upon the character of the ground 

 where they have grown. In the specimen of Retepora columnifera which I have 

 examined, there are chitinous tubes in the interior of these dorsal processes, looking at 

 first as if they were produced by the Retepora, but they are the chitinous tubes of a 

 Caherea or Scru2)0cellana, and the Retepora has attached itself to the Caberea. By 

 such means a Retepora might grow to considerable dimensions over ground that was 

 unsuitable for direct attachment. 



Surrounding the zooecia at a slight distance from the surface, is a tube which is 

 partly filled with a cellular cord. This' parenchymatous cord is common to the whole 

 zoarium, but communicates with the zooecia by means of threads near the oral aperture, 

 and perhaps we shall find them elsewhere. This is seen in decalcified preparations ; also 

 in sections of the calcareous structure the hollow tube which contains it is very distinct 

 near the anterior surface, but no indication is given on the surface of such a tubular 

 structure ; however, in Retepora couchii it can be seen in the " slightly raised tubular 

 border" between the zooecia, which I described in Ann. and Mag. Nat. Hist., ser. 5, 

 vol. iii. p. 200. When describing Retepora couchii I decalcified specimens without 

 finding the explanation, but perhaps I had unsuitable material, as I now can trace it. 

 Although I have examined a considerable number of species without finding this common 

 zoarial cord, yet I expect that it will be found in several Reteporae. Jullien^ says that 

 Retepora and Catenicella are for him only words representing colonial forms and not 

 generic forms, but both these genera shows important characters independent of the 

 colonial form ; with Reteporxt Hincks has pointed out several, and I have done the 

 same with Catenicella, but for Retepora I would now point out another. The shell 

 structure shows lines of deposition in a distinct way, which is peculiar to the genus, and 

 besides the shell is not continuous but encloses hollow spaces or lacunae. This is 

 specially marked in Retepora lata, and is distinct in Retepora cellulosa ; but in pointing 

 out fresh characters, it must not be supposed that the present boundaries of a natural 

 group may not have to be altered with extended knowledge. 



Retepora avicularis, MacGillivray. 



Retepora avicularis, MacGillivray, Trans. Eoy. Soc. Vict., vol. xix. p. 288, pi. ii. fig. 6 ; Zool. 



of Vict., dec. x. p. 16, pi. 94, fig. 16; pi. 95, figs. 7-11. 

 Retepora jacksonieiisis. Busk, Zool. Chall. Exp., part xxx. p. 125, pi. xxvii. fig. 4. 



In the Challenger specimens the ovicell has not been noticed, but as the other, 

 characters correspond with Retepora avicularis, it would seem that it is identical with 

 that species from Victoria. 



Habited. — Victoria ; New South Wales. Fossil — Mount Gambler. 



' The specimen examined was dry. 2 Bryozoaires, Mission du Cap Horn, p. 5. 



