SPONGES. 119 



The geographical distribution of Xenospongia patelliformis is, as pointed out by 

 Holdsworth (9), very interesting; the only records up to the present time being 

 Torres Straits and Ceylon. That the specimens met with in these two localities are 

 specifically identical, 1 have little doubt. Gray, in describing the species from 

 Torres Straits, gave no description of the spicules, and did not even mention the 

 occurrence of asters. Carter, to some extent, remedied this defect in 1882 (33). but 

 he only figured two forms of aster, and those not very characteristic. His 

 microscopical preparations, however, which are now in my possession and which were 

 presumably made from one of the Torres Straits specimens (for Holdsworth's 

 specimen and record from Ceylon appear to have been entirely lost sight of ever since 

 his note on the subject was published), show both large and small asters of various 

 forms, and the actines of the large ones may occasionally branch. Mr. Carter's 

 preparations are only teased ; had they been boiled out from all parts of the sponge, 

 they would probably have shown all the forms of aster described above from 

 Professor Herdman's example. 



The external form is, of course, extremely characteristic, and so little does it look 

 like a sponge that the specimen described above was in the first instance placed 

 amongst the Clypeastroids. 



R.N. 375. (Stat, I. First haul of trawl, off Negombo, 12 to 20 fathoms, January 

 31, 1902.) 



Family : SPIEASTEELLID.E. 



Astromonaxonellida usually of massive or encrusting form. Skeleton usually irregular 

 or reticulate, at any rate internally. Megascleres usually stylote or tylostylote. 

 Microscleres asters of various forms. 



Hymedesmia, Bowerbank. 



Thin encrusting Spirastrellidae whose spiculation consists of smooth tylostyli and 

 euasters of various forms (occasionally passing into spirasters). 



Topsent has given an excellent account of the literary history of this genus in his 

 Monograph of the Sponges of France (14). A very large proportion of the known 

 species come from the Gulf of Manaar, and were described by Mr. Carter (4) in 

 1880 : viz., H. stellivarians, H. moorei, H. spinatostellifera, H. capitatostellifera, and 

 H. trigonostellata. Of these five species I have only met with one in Professor 

 Herdman's collection. 



The genus is an extremely interesting one from the phylogenetic point of view, for 

 we see here, in the first place, the first appearance of the characteristic suberitid 

 " pin-head" spicule (tylostyle), and, in the second place, the evolution of the typical 

 spirastrellid microsclere from the euaster. 



Hymedesmia forms a connecting link between Coppatias and Spirastrella, 



