236 DISCOVERY REPORTS 



circular. Tubes ending blindly below, their basal parts held together by common 

 coenoecial substance, which is very soft and spongy and sometimes encrusted with sand 

 grains. Zooids greyish white, orange or brown. Length of a fairly extended zooid from 

 tip of arms to base of body 4 to 7 mm., length from base of arms to end of body 2 to 

 4 mm. Arms, usually eight pairs, no end-swellings. Male, female and hermaphrodite 

 zooids found in the same colony. Testis elongate and pyriform. Buds, six to twelve on 

 each zooid. 



Locality. 



St. 82. 20. vi. 26. 32° 42' 00" S, 2° 05' 00" W. Gear N200. 75 (-0) m. One specimen. 

 St. 190. 24. iii. 27. Bismarck Strait, Palmer Archipelago, 64° 56' 00" S, 65° 35' 00" W. Gear 

 NRL. 126 m. Two specimens. 



St. WS 82. 21. iii. 27. 54° 06' 00" S, 57° 46' 00" W. Gear OTC. 140-14401. One specimen. 



The coenoecium of the small piece obtained from station 82 is very much damaged 

 but the zooids are in an excellent state of preservation. The two specimens (broken pieces 

 of colonies) from station 190 are well preserved and the tubes undamaged (PL XXXIII, 

 fig. 6). The common coenoecial substance and tubes of one of the specimens contain 

 sand grains, fragments of shells and sponge spicules. 



The colonies of C. densus are formed by closely set, vertically directed tubes which are 

 held together in the basal region by common coenoecial substance. Since the present 

 collection is formed only of fragmentary pieces, nothing definite can be said about the 

 shape of entire colonies. As the tubes are closely set, and new tubes are formed only at 

 the periphery, the colony increases in bulk laterally. If new tubes are formed uniformly 

 all over, a large colony may have a flat cake-like appearance, but if growth on any one 

 side is obstructed, the colony may have a more or less irregular outline. If this is proved 

 to be the case, the shape of the colony can be regarded only as a secondary factor, de- 

 pending upon the rapidity with which new tubes are added in any particular region and 

 the presence or absence of obstruction near any part of the colony. On a plane sub- 

 stratum, the colony may extend equally on all sides and assume the perfect shape recorded 

 by Ridewood. 



The thickness of the wall of the tube varies. In the specimen obtained from station 82 

 the external diameter of the tube is 1-3 mm. and the internal diameter i mm. But the 

 external diameter in the specimen obtained from station 190 is i-6 mm., and the internal 

 diameter is only slightly less, the tubular wall being very thin. The tube ends blindly 

 below in the common coenoecial substance and at the upper free extremity opens by 

 a transverse circular ostium devoid of any kind of lip-like outgrowth. They are slightly 

 irregularly curved in the long axis, but there are a few straight tubes in the colony. The 

 smooth inner lining of the tube is formed of thin rings. These are surrounded by an 

 outer layer of irregular thickness. When a tube is dissected out in order to remove the 

 zooids, the outer layer peels off easily, but the thin inner layer adheres closely to the 

 visceral mass of the zooids, so that often it cannot be removed without damaging them. 



Andersson (1907, p. 12) separates C. densus from C. rarus by the nature of the tubes. 



