﻿28o "ENDEAVOUR" SCIENTIFIC RESULTS. 



EcHiNOCLATHRiA ARBOREA, Leudenfcld. 

 (Plate xxix. , fig. 2, and fig. 63.) 

 1888. Plectispa arhorea, Lendenfeld, Cat. Sponges Austr. 

 Mus., 1888, p. 226. 

 [Not Clathria {Plectispa) arhorea^ Whitelegge, Rec. 

 Austr. Mus., iv., 2, igoi, p. 88.] 

 1901. Echinoclathria elegans, Whitelegge, Loc. cit., p. 90. 

 [Not Plectispa elegans, Lendenfeld, Cat. Sponges 



Austr. Mus., 1888, p. 226.] 

 Sponge stipitate, arborescent, branching dichoto- 

 mously ; branches elongated, cylindrical, averaging 7 

 tJim. in diameter, seldom anastomosing. The superficial 

 cell-apertures are not bounded by lamellce disposed edge- 

 wise to the surface: normally, they are circular or oval 

 in outline, and, on the average, are less than 2 mm. in 

 width and. about the same distance apart; but in some 

 specimens the trabeculce are rod-shaped, and the structure 

 is then no longer cellular, but clathrate. Main fibres 

 with a paucispicular core; connecting fibres either imth 

 uniserially arranged spicules, or vacant. Echinating 

 spicules most abundant upon, but not restricted to, the 

 superficial fibres. Auxiliary megascleres variable in 

 number, sometimes rather scarce. Megascleres {similar 

 inform to those of E. ramosa): — (i.) Principal styli vary- 

 ing in maximum size in different specimens from 100 x 

 ^.5 to 120 X 7 ii; {ii.) auxiliary strongyles, maximum size, 

 IJ5 X I.J ji. ChelcB {apparently) absent. 

 Introductory. — I have already pointed out (p. 204) that the 

 sponge identified by Whitelegge as Plectispa elegans is cer- 

 tainly not that species, and have indicated the chief reasons 

 for regarding it as identical with Lendenfeld's Plectispa 

 arborea. These reasons perhaps require to be more explicitly 

 stated. Concerning Plectispa arborea, Lendf., one can draw 

 the conclusion from what Lendenfeld has written, that the 

 species is possessed of a structure in some way analogous to 

 that which is characteristic of Echinoclathria — and, more par- 

 ticularly, of such species as E. ramosa: for the sponge is 

 described as "dendritically ramifying ;" and in the diagnosis of 

 the genus Plectispa we are told that the sponges belonging 

 thereto are "elegantly reticulate." The account of its spicu- 

 lation also, lends support to the opinion that the species 

 belongs to Echinoclathria. Consequently, considerable im- 

 portance attaches to the statement that the sponge has— an 

 unusual feature amongst the species of Echinoclathria-— a 

 "clearly-defined stem." As to the precise nature of the reticu- 

 lar structure of P. arborea, the description omits to inform us : 

 the omission, however, affords reason for supposing that the 

 external appearance of the sponge is, at any rate, not altogether 



