28o "ENDEAVOUE" SCIENTIFIC EESULTS. 



EcHiNOCLATHRiA ARBOREA, Lenclenfcld. 

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

 1888. Plectispa arborea, 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. cil., p. 90. 

 [Not Plectispa elegans, Lendenfeld, Cat. Sponges 



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

 Sponge stipitate, arborescent, branching dichoto- 

 niously ; branches elongated, cylindrical, averaging 7 

 mm. 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 

 ividth 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 zvith 

 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 

 in form to those of E. ramosa): — (t.) Principal styli vary- 

 ing in maximmn size in different specimens from 100 x 

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

 135 .\- I.J ]i. ChelcE {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 explicitl}- 

 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 

 "clearlv-defined stem." .^s 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 



