SYSTEMATIC ACCOUNT 233 



In his description of C. inaeqiiatus, Andersson (1907) says that female zooids have ten 

 arms and males twelve. This is contrary to my observations and may strengthen the 

 claims of Andersson for regarding C. inaeqtiaUis as a distinct species. But since the 

 classification of Cephalodisais is based mainly on the structure of the coenoecium, the 

 close resemblance between the coenoecium of C. inaeqiiatus to that of C. hodgsoni makes 

 the line of demarcation very faint. 



Sub-genus Idiothecia 



Cephalodiscus nigrescens, Lankester. 



Lankester, 1905. 



Ridewood, 1907 b, 1918 a and 1918 b. 



Gravier, 1913. 



Diagnosis. Colony massive, branching; maximum width of a single branch 5 to 

 9 mm., branches roughly cylindrical. Colour greyish, translucent. Ostia placed at the 

 end of peristomial tubes, but in the main stems frequently sessile. Abaxial edge of 

 peristome produced into a blunt lip. No spines. Each ostium leading into a tube which 

 ends blindly in the middle of the branch. The length of the peristomial tube depends 

 on the thickness of the branch. The lower part of the tube is curved downwards slightly 

 and shut off by a septum, so that the zooids inhabit the upper region only. Width of 

 the cavity of the peristomial tube 1-2 to 1-3 mm.; length 14 to 21 mm. Length of the 

 zooid from free end of the body to tip of arms 4 to 6 mm. Preserved zooids blackish, 

 with six or seven pairs of arms. Each arm with two longitudinal black bands running 

 along the whole length of its axis. Arms without end-swellings. Male, female and 

 hermaphrodite zooids occurring in the same colony. 



Locality. 



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

 DLH and NRL. 93-126 m. Large quantities. Gear DLH. 315 m. One specimen. 



It is interesting that C. nigrescens was dredged from the same station which also yielded 

 a good collection of C. hodgsoni. Much material was dredged from the depth 93 to 

 126 m. and only one piece of a branch from a depth of 3 15 m. No differences in structure 

 or colony formation were observed between specimens from the two depths. 



Colonies of C. nigrescens are formed of branching cylindrical stems of varying thick- 

 ness. The test^ is gelatinous and almost transparent in the growing regions. 



The older parts are greyish brown with a maximum transverse measurement of 30 mm. 

 The minimum width of a branch is 5 to 9 mm. The ends of the branches are either 

 blunt or tapering. 



^ The continuous cavity found in Demiothecia, occupied in common by the zooids, is replaced by a number 

 of small tubes in Idiothecia, each occupied by one zooid and its buds. These are embedded in a common 

 mass of coenoecial substance. Because of this differentiation, Ridewood (1907 b, p. 21) introduced the term 

 "Tube" for the individual cavities occupied by the zooids (instead of cavity) and "Test" for the common 

 mass of coenoecial substance (instead of coenoecium). 



