474 



COLLECTIONS FROM MELANESIA. 



in the arm is not quite constant in its position. The rest of the 

 characters agree with those of the typical form. 



Hah. West Island, Torres Straits, 7 fms. ; bottom sand. 



Variations. This sponge varies, as has been seen, in shape (oval 

 or subspherical) and in the presence or absence of a vent. A third 

 variation may be noted, viz. in the length, stoutness, and amount 

 of curve in the arms, and in stoutness of the shaft of the zone- 

 spicule ; thus in a specimen from the Arafura Sea the diameter of 

 the shaft falls to '045 millim., that of the arms to "043 millim., the 

 length of the arm remaining '25 millim., while the backward bend of 

 the arm, though gradual, is very decided. 



The variations in this spicule, which is the only one which seems 

 to differ much in different specimens, are as follows : — 



1. Port - Darwin speci- 



men 



2. Thursday Island spe- 



cimen 



3. Arafura -Sea speci- 



men 



4. Var. retrqflexa (West 

 Island, Torres Straits) 



Curve of arm 



slight, gradual. 



» » 



decided,gradual, 



sharp near end. 



The stellate is only "013 to # 0l7 millim. in diameter in specimen 

 No. 3. 



The species differs from >"?. bacca, Selenka, in the small size of the 

 stellate spicule, viz. -02--025 millim. instead of -2 to *4 millim. in 

 diameter ; from S. tethyopsis, Carter, in having no " forks," and 

 simple, not trifid, arms to the " zone-spicule ; " and from S. globo- 

 stellata, id., in the absence of a globostellate spicule ; for distinctions 

 from other species see table of species above. The largest specimens 

 measure about 25 millim. (1 inch) in greatest diameter ; all the 

 specimens are preserved in spirit. 



102. Stelletta clavosa *. (Plate XLIII. figs, i, i".) 



Free, subglobular (very occasionally suboval). A single circular 

 vent is almost (if not quite) invariably present ; it is situate either 

 on a flattened or depressed area ; its margin apparently forms a 

 sphincter ; diameter 2 millim. in the largest specimens received. 

 The excretory canals unite at 1-2 millim. below surface. Colour, in 

 well-preserved spirit-specimens, pale purplish grey to puce, in others 



* From clavus, a nai!, in allusion to the fine nail -like zone-spicule. 



