SPONOK8. 1 1 5 



Xenospongia, GRAY. 



Tethyiche of discoidal form. Choauosome containing much sand in its deeper parts. 

 Inhalant pores localized in well-defined grooves, partly concentric and partly 

 radial in arrangement. Vents on slight prominences. Surface tul>erculate. 

 Skeleton composed of bundles of styli ending in brushes, which project from the 

 surface tubercles and also form a slight marginal fringe. Microscleres euasters 

 of various forms and sizes, forming a dense cortical layer, and also abundantly 

 scattered in the choanosome. 



The genus Xenospongia was established by GRAY (30) as far back as 1858 for the 

 reception of two remarkable sponges from Torres Straits, of which he gave a very 

 poor description accompanied by excellent figures of the external characters only. 

 He made no attempt to describe the spiculation, and, although this defect was 

 partially remedied by CARTER in 1882, our knowledge of the sponge has remained 

 singularly incomplete up to the present day. The genus has only been recorded 

 once since its original discovery, viz., by HOLDSWORTH (9) from the Ceylon pearl 

 banks in 1873. No description, however, has ever been published of HOLDSWORTH'S 

 specimen, and the identification with GRAY'S species, though doubtless correct, was 

 quite unsupported by evidence. HOLDSWORTH'S record and specimen (which appears 

 to have been forwarded to GRAY for further investigation) both seem to have been 

 lost sight of by subsequent writers. 



Under the circumstances, it is not remarkable that the systematic position of 

 Xenospongia has hitherto remained doubtful. GRAY himself, in 18(58 (31), made it 

 the type of a new family, for which he proposed the name " Xenospongiadae." 

 CARTER, in 1875 (32), referred it to his group " Donatina," along with Tetliya 

 lyncu'rium, but expressed the opinion that it might ultimately have to come amongst 

 the "Suberitida." In 1882, however, this author (33) reverted to GRAY'S opinion, 

 and proposed " a group named Xenospongina = Xenospongiadse, GRAY." SOLLAS, in 

 1888 (15), referred the genus doubtfully to the Tethyidse, pending further informa- 

 tion. TOPSENT, in 1898 (26), made a new departure by referring it to the 

 Spirastrellidse, though, as it seems to me, with very slight justification. 



The minute investigation which I have been able to make of Professor HERDMAN'S 

 well-preserved specimen proves beyond doubt that the opinion of SOLLAS is correct, 

 and that Xenospongia is very closely related to Tethya itself, alike in spiculation, 

 skeleton arrangement, histology, and canal system, although the external form and 

 the arrangement of the inhalant pores are very peculiar. Even the surface tubercles 

 or conuli, and the somewhat pinkish colour in spirit, remind one strongly of the genus 

 Tethya. In Tethya also one sometimes sees the beginning of the development of 

 pore-bearing grooves between the conuli, and the branching of the rays of the 

 asters, which takes place so extensively in Xenospongia, may also be observed 

 occasionally. 



