OF THE SPONGIAU^. 183 



Sponge massive, suborbicular. Skeleton consisting of 

 fasciculi of spicula. Fasciculi radiating from a basal 

 or excentrical point to the surface. Intel-marginal 

 cavities unsymmetrical, confluent. Propagation by 

 internal or external gemmulation. 



Types, Tethea lyncurium, Linnaeus, &c. 

 cranium, Lamarck. 



This genus affords ns one of the few instances in which 

 we may avail ourselves of external form as a generic 

 character; but even in Tct/iea we approach exceptions to 

 the rule in the depressed form of T. Collinysii, Bower- 

 bank, as exhibited in the only perfect specimen of that 

 species which I have seen, and in the still more depressed 

 form of T. spinularia, Bowerbank. 



Although the skeleton structures in the species of this 

 genus differ to an exceedingly slight extent, the subsidiary 

 spicula vary exceedingly in the different species. In some, 

 tern ate spicula are numerous, and in others they are entirely 

 absent, and stellate forms of spicula occur in many varieties 

 of form. 



The sponges of this genus appear to be highly organized. 

 Audouin and Milne- Edwards saw the oscula open and the 

 excurrent streams in action, and I have seen the same 

 myself in a specimen of T. lyncurium. My friend Mr. 

 George Clifton, of Freemantle, Western Australia, in a 

 letter dated 25th January, 1861, writes, "I have sent you 

 several fine specimens of Tethea. When these animals 

 are first taken out of the water they are of a brilliant orange 

 colour, and commence squirting water from the oscula 

 situated on the centre of the upper surface ; they also 

 contract considerably, but on being replaced in their native 

 element they regain their natural size and reabsorb water." 



The mode of propagation varies in different species. In 

 T. cranium and simillima, Bowerbank, MS., it is by internal 

 gemmulation, in T. lyncurium by external gemmulation, and 

 "in some other species the mode is not apparent. 



Figure 362, Plate XXXI, represents a portion of a slice 

 at right angles to the surface, from Tethia cranium, showing 



