24 . H. KlKKl'ATlilCK. 



Family Desmacidonid.-e, Ridley and Dendy. 



I. Sub-Family Ectyonin-k, Ridley and Dendy. 



Hymedesmia arkolata. 



(Plate XXII., fig. 3-3c.) 



1905. Hymedesmia areolata Tliiele (23. p. 452). 



There are two specimens, one a fine large one, the other a small nodule ; hotli have 

 a broken surface, and on the lahel is the legend " Broken ofi" a stone." 



The larger .specimen is an oval mass 12*5 cm. long, G'5 cm. high, and 5 "5 cm. 

 thick. 



The species is easily recognised from the areolated appearance of the surface. 

 There are numerous oval or circular poral pits, 1-5 mm. across, with over-hanging 

 edges ; the concave floor is perforated with pores. 



The densely packed ectosomal oxeas ai-e arranged radially round the pore pits. 

 The oscules are small inconspicuous cones contracted to a point. 

 The flagellated chambers are aphodal, 36 x 23 /a in diameter. 

 Thiele's specimens were in the form of incrustations on chitinous tubes. 

 The 'Discovery ' specimens were dredged near Winter Quarters in 12| fms. 

 The species has also been recorded from Calbuco, Chile, 40 metres (Thiele). 



Hymedesmia exigua. 

 (Plate XXII., fig. 4, and Plate XXVL, figs. 2a-f.) 

 l',)07. Hymedesmia cxiyua Kirkpatrick (10a. p. il'X). 



Description. The sponge forms a thin translucent grayish-white crust, about 

 5 mm. in diameter, on a stone. The surface is smooth, and the substance of a fleshy 

 consistence. 



The skeleton. The choanosome contains scattered short acanthostyles, and the 

 dermal memljrane tangential tylotes isolated or in bundles of a few. 



Spicules. Megasclcres. Acanthostyles, 94 x 19 /a, short, thick, with spines 

 pointing Itackwards slightly. Ectosomal tyles, 157 X 3*5 jn, straight, smooth, with 

 oval heads, 5 /a long, and 4 • 5 /a broad. 



Microscleres. Pluridentate isancorae spatuliferae ; with five foliate teeth, 5 fj. in 

 length, at each end, sometimes with three or four; shaft deeply curved, 2"5 /a thick, 

 sometimes with central alate expansions. 



Sigmata 9 • 6 /a long, 5 • 6 broad, • 5 /a thick, scattered separately in the choanosome. 



Tlie new species resembles in several respects //. zetlamlica Bowerbank, but the 

 anconic of the latter have only three teeth, the sigmata are much longer (51 fj.) and 

 in .sheaves; also the ectosomal tyles are much larger, viz., 328 x 3 "25 /a, and 

 the spines of the acanthostyles more vcrticillate. Jfi/medesmia irritans Thiele, from 



