Mr. H.J.Ct ■ ^ *hp. Snongida. 163 



world for a seaweed to become a pseudomorph of a sponge i^iv/ 

 use a mineralogical term), in wliicli the latter, like a "dis- 

 solving view," may be observed (through different specimens) 

 to yield gradually to the former, so that, at last, the seaweed 

 not only assumes the shape of the sponge generally, but that 

 of the form and position of the vents and every other part of 

 the sponge saving the spicules, or foreign bodies of a like 

 nature, which thus are often the only remaining evidence of 

 the kind of sponge that has thus been pseudomorpliosed. 



I noticed this first in specimens of Renter a Jihidata, Sdt., 

 from Hong Kong, in the British Museum, wherein parts of 

 the sponge itself still remained to prove what has been just 

 stated ; and since then several specimens have been added 

 from the late Dr. Bowerbank's collection, that were obtained 

 from Freemantle on the south-west coast of Australia — which 

 led me to seek for the seaweed in Harvey's ' Phycologia 

 Australica,' where I found it figured under the name of 

 " Thamnoclonmm jlabelliformej'' also from Freemantle (vol. ii. 

 pi. 13). 



The fan-shaped pseudomorphs in the British Museum 

 represent the figure, and bear remains of the spiculation of 

 this form of Echinonema iypicum, Cart. MS., which is very 

 common at Freemantle ; another, that of a Suberite with pin- 

 like spicules only (that is, without any flesh- spicules) ; and a 

 third bears on its surface portions of the reticulated incrusta- 

 tion of foreign bodies characterizing many of the Psammone- 

 matous sponges. 



Frequently, as stated by Harvey, on the more prominent 

 parts of this parasitic seaweed may be observed little pedi- 

 celled leaf-like expansions or young fronds, which, when sof- 

 tened by soaking in water, present " tetraspores lodged in 

 discoid nemathecia, in their substance ;" and thus far the 

 reproductive elements of this Alga have been discovered. 



Red Alga parasitic in Halichondria plumosa, 

 Johnston. 



There is an amorphous Alga (apparently undescribed) 

 Avhich infests some specimens of Halichondria plumosa on 

 this coast, consisting of a pseudofrondaceous expansion of 

 carmine-red cells, which, pursuing in its growth the main 

 branches of the skeleton, from the base to their termination 

 on the surface of the sponge, finally produce a dark-brown- 

 coloured, equally amorphous, wart-like fructification. 



Its cells are irregularly globular, of a beautiful carmine 

 colour, and held together by a gelatinous membrane, which 

 not only grows upwards round the axis of the branches men- 



11* 



