REPORT ON THE MONAXONIDA. 39 



Sigmata about 0"04 by 0"0015. It is needless to give furtber details conceruiug au already 

 well-known species; the reasons for uniting Halichondria varia, Bowerbank, and Isodictya 

 virgata, Bowerbank, bave already been given by Eidley in the " Alert" Report {loc. cit.). 



Locality.— Station 208, January 17,1875; lat. 11° 37' N., long. 123° 31' E.; Philip- 

 pine Islands ; depth, 18 fathoms ; bottom, blue mud. A number of fragments. 



Habitat. — Strait of Malacca (Bowerbank) ; Port Darwin (Ridley) ; Philippines 

 (Challenger), 



Gellius carduus, Ridley and Dendy (PL VIII. fig. 3 : PI. XIII. fig. 7). 



1886. Gellius carduus, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xvLii. p. 333. 



Sponge (PI. VIII. fig. 3) sessile, more or less oval, or egg-shaped. Size of the 

 two most perfect specimens about 33 mm. long by 20 mm. broad. Colour in 

 spirit pale greyish-yellow. Texture loose but firm. Interior of the sponge cavernous, 

 owing to the numerous wide canals by which it is traversed. Surface raised into 

 numerous angular prominences, many of which have oscula at their summits. Dermal 

 membrane distinct, hyaline, covering large subdermal cavities, and pierced by numerous 

 scattered pores, about 0"052 mm. in diameter. Oscida scattered singly on the summits 

 of angular prominences. 



Skeleton. — (a) Dermal; consisting of a very beautiful unispicular reticulation of 

 large, stout, blunted oxeote spicules (exhibiting occasionally a tendency to form loose, 

 long fibres), {b) Main; consisting of a loose reticulation of similar spicules, not 

 united to form definite fibres. Hence the firmness of the sponge is due rather to the 

 large amount of tough membranes present, supported by loose spicules, than to the presence 

 of any definite spiculo-fibre. 



Spicides. — (a) Megasclera ; of one kind only, viz., blunted oxea (PL XIII. fig. 7), 

 slightly bent, and tapering to a rounded extremity at each end. Size 0*6 by 0'023 mm. (b) 

 Microsclera ; numerous small sigmata of the usual shape, measuring 0'02 by 0"0012 mm. 



This species is readily distinguished by its very characteristic external form, the 

 surface resembling that of a large thistle-leaf, whence the specific name. The shape of 

 the skeleton spicules is also very characteristic ; they might be described as strongjda, 

 tapering slightly towards each end ; but there can be no doubt that they are simply 

 blunted oxea. 



Localities.— Station 148a, January 3, 1874 ; lat. 46° 53' S., long. 51° 52' E.; depth, 

 240 to 550 fathoms ; bottom, hard ground, gravel, shells. One specimen, attached to a 

 pebble. 



Ofi" Prince Edward Island, December 27, 1873; depth, 85 to 150 fathoms. Three 

 specimens. 



Olf Marion Island, 50 to 75 fathoms. One specimen. 



