676 " THETIS " SCIENTIFIC RESUIiTS. 



very closely related. The only noteworthy difference, as it 

 seems to us, lies in the character of the spicules. Roule lays 

 emphasis on the mode of branching, which he finds to be more 

 sparse in W. elongata than in M. dichotoma, and with a strong 

 tendency to the formation of long, simple branches. Our new 

 species, M. australis, agrees with Roule's desci'iption of the 

 branching of M. elongata, but it also agrees with the undoubted 

 specimens of M. dichotoma in the present collection — so closely, 

 indeed, that it was at first mistaken for that species. We do 

 not think that the mode of branching can here be safely used as 

 a specific distinction. Perhaps the same is true in regard to the 

 details of spicule-form. 



Locality. — Eleven miles east of Broken Bay, 



MOPSEA FLABELLUM, sp. nov. 



(Plate Ixiii. figs. 1-3 ; pi. Ixvii. fig. 6 ; pi. Ixxi.) 



Stations 34, 44. 



This species is based on one complete colony and a number of 

 pieces. 



The complete specimen rises from a slightly encrusting cal- 

 careous base to a height of 24-5 cm. Branching begins at a 

 height of 55 cm. and is very luxuriant ; the branches are con- 

 fined almost exclusively to one plane, and there is a strong 

 tendency to dichotomy ; they are slender throughout, and 

 do not taper much ; the stouter branches have a diameter 

 2 "5 mm., and the twigs of almost 2 mm., near their tips. 



Near the base the diameter of the axis is 4 mm. Here the 

 ccenenchyma has been worn of}, and the bulk of the stem is 

 made up of the horny joints which are about 2 mm. long, the 

 calcareous joints being reduced to -75 mm. ; in some cases they 

 are quite overlapped by the horny joints. Higher up the cal- 

 careous joints have lengths of 3-4 mm., and the horny joints "25- 

 •5 mm. The colour of the horny joints is brown ; that of the 

 calcareous joints varies from cream-white near the base of the 

 colony to orange in the twigs. The calcareous joints bear marked 

 longitudinal flutings. The branches arise from the calcareous 

 joints. 



The polyps occur in close-wound spirals all over the stem 

 and branches. In the youngest twigs the spiral is wider but 

 nowhere is there any trace of a bilateral arrangement. The 

 polyps are club-shaped, with somewhat truncate mouths which 

 are pressed against the cortex of the branch. The average 

 length of a polyp is 1 mm. The calyces are armoured with about 

 eight rather indefinite longitudinal rows of overlapping spicules,. 



