TETHYA. 41 



his T. Zetlanclica ; and Mr. Carter himself now doubts 

 whether that form is entitled to specific rank (' Ann. 

 Nat. Hist.,' ser. 4, vol. xviii, p. 471). I have spe- 

 cimens in rny collection which closely agree with the 

 characters of Zetlanclica, but I am inclined to regard 

 them as cranium in which the dermal membrane and 

 subdermal sarcode with their bihamates have been 

 washed away; while the consequently outstanding 

 fasciculi of radiating porrecto- and recurvo-ternate 

 spicula, of which the apices are broken off, give the 

 sponge the " thick-set papillae" which render it so 

 different in appearance to the naked eye from the 

 silky investiture of the same sponge when in fine 

 condition. The differences in the gemmules appear 

 to be those which had previously been noticed by 

 Bowerbank. 



I now proceed to notice the forms which have been 

 met with. 



TETHYA CRANIUM, var. 1, TYPICA. 



The externally protruded spicula, arranged in whorls 

 like the hair of the human head, and presenting a 

 hoary, shining, asbestine appearance. The sarcode, 

 abundantly supplied with excessively minute sigmoid- 

 bihamate spicula (magnified 1166 diameters, in, PL 

 XIY, fig. 5), measuring about -^Vs inch long. " The 

 spiral twist of the spicules and presence of bihamates 

 are as characteristic of the young while still within 

 the body of the mother as they are of the adult ' 

 (Carter). 



