650 



mounted slide of the spicules of a Port Pliillip sponge in which 

 (while otherwise closely agreeing in spiculation with D. lunata) 

 the microxea for the most part are more or less curved in a dis- 

 tinctly sigmoidal manner.* There is evidence for supposing, 

 therefoi'e, that the microxea of Desmoxya are derivatives of 

 sigmata. 



Desmoxya lunata Carter. 

 (PI. xxix., fig.5; PL xxxviii., fig.5; PL xliv., fig.4.) 



1885. Hiyginsia lunata Carter(5), p. 358. 



1897. Hiyginda hmafa Dendy(7), p.244. 



Diagnosis. — Sponge massive, sessile, moi-e or less dome-shaped, 

 rising above into short digitiform processes, and provided also 

 with irregularly scattered small conuli. Dermal membrane 

 minutely reticulate; with many dermal pores in each mesh of 

 the reticulation. Skeleton feebly developed, consisting of irregu- 

 larly ascending, slender, multispicular main fibres, between which 

 thei'e extends a very sparse and irregular reticulation composed 

 chiefly of single spicules. Megascleres slightly curved, cylindrical 

 or nearly so; comprising oxea and styli in approximately equal 

 numbers, and relatively few strongyla; maximum size about 800 

 by 12 to 15/x. Microxea crescent-shaped, minutely spinulous 

 except in their central moiety, 30 to 45/x long and up to 3'5/x in 

 stoutness. Tricliites separable into two groups as I'egards size, 

 the shorter varying from 60 to 220/i. in length, the longer from 

 560 to 620//.; occurring in dragmata and scattered singly, the 

 larger ones also forming short fibres. 



Xoc— Port Phillip. 



External features. — The sponge (which is known now from 

 seven examples) appears always to be more or less dome-shaped 

 (PL xxix., fig.5), — usually not far from (roughly) hemispherical, 

 sometimes nearly as high as broad, occasionally, however, much 

 depressed, almost flattened, — and is provided with moderately 

 numerous mammiform, or short digitiform, processes; in addition, 



* In this presumable second species of Desmoxya, the microxea (if they 

 may correctly so be termed) are very small, rarely attaining to more tlian 

 25u in length. 



