412 Mr. H. J. Carter on two new Sponges 



great resemblance of one sponge to another, I never now am 

 content to decide in this respect until I have actually examined 

 microscopically a bit from the sponge itself presented to my 

 notice. Thus, in examining all the six specimens mentioned, 

 I came upon four, distinctly different from Tethya cranium^ 

 Johnston, which has been so aptly named and figured with its 

 oviform bodies by this accurate naturalist (Hist. Brit. Spong. 

 &c. 1842, p. 83, pi. 1. figs. 1-8). 



From the label on the jar, it is therefore evident that both 

 species inhabit the sea about Shetland, having probably 

 come from the " Haaf Banks ;" for Dr. Bowerbank states 

 that he obtained "nearly three hundred specimens" that were 

 dredged up there (B. S. vol. ii. p. 84). 



For this new species, which will presently be described, I 

 propose the name of Tethya zetlandica (PL XXII. fig. 1). 



As all the specimens, viz. both T. cranium and T. zetlandica^ 

 are filled with ova in different stages of development, I took 

 the opportunity of mounting some of the more advanced ones 

 in Canada balsam, and found that they possessed the same 

 distinguishing characters which point out the difterences be- 

 tween the adult forms of both these species. 



Moreover the presence of the ova in different stages of 

 development from a very early period has enabled me to give 

 descriptions and illustrations of a sequence of them, preceded 

 by zygosis in the sponge-animals, taken from Halichondria 

 simulansy Johnston, in the living state, which thus far seems 

 to point out the mode of sexual reproduction and development 

 in the Spongiada generally. 



The zygosis takes place by apparent union of the "collars" 

 of two sponge-animals, animalcules, or infusoria (whichever 

 name pleases best), so that their "rostra" are brought into 

 apposition just like that witnessed in the Difflugice, where the 

 mouths of the two tests are brought together by an apparent 

 union of the contained animals. Of course it will be necessary 

 to give a detailed account of zygosis in the Diffiugice to com- 

 pare it with that of the sponge-animalcule. 



For the terms " collar " and " rostrum," see my description 

 and illustrations of the sponge-animal (Annals, 1871, vol. viii. 

 p. 9, phi. fig. 13, ^.). 



I shall also at the same time be able to add a few more ob- 

 servations on the development of the spicule. 



Tethya antarctica^ n. sp. PI. XX. 



Body globular ; colour tawny yellow. Surface smooth, in- 

 terrupted frequently by papillaj, through which the spicules of 

 the interior project in bundles, cactus-like (PI. XX. figs. 1 



