DESCRIPTION OF SPECIES 47 



this is not so (see below). If S. adareanum extends to South Georgia, and I have here accepted several 

 specimens from that area as S. adareanum, the small size of these specimens might be explained by 

 less favourable conditions prevailing on the boundary of the geographical range. 



Distribution. Antarctic (Graham Land, South Shetlands, South Georgia, Ross Sea, Kaiser 

 Wilhelm II Land, Enderby Land, Adelie Land, MacRobertson Land), Subantarctic (Kerguelen). 



Synoicum georgianum Sluiter (Text-fig. 7 A, B, C, D; PI. I, fig. 7) 

 Synoicum georgianum Sluiter, 1932, p. 11, figs. 9, 10. 



Occurrence. St. 140: S. Georgia, 122-136 m. St. 144: S. Georgia, 155-178 m. St. 149: S. Georgia, 

 200-234 m. St. 474: S. Georgia, 199 m. St. 1941: S. Georgia, 55-22 m. St. WS794: Patagonian 

 Shelf, 123-126 m. St. MS 10: S. Georgia, 26-18 m. St. MS 74: S. Georgia, 22-40 m. 



Colony (Text-fig. 7A; PI. I, fig. 7). The colonies are all small, never exceeding 2-5 cm. in length. 

 Two, three or four heads generally arise from a common base, are narrow in their lower part and 

 gradually widen towards the distal end. Some colonies consist of many small heads attached to a mass 

 of basal, somewhat root-like processes, a condition approaching that described by Sluiter for the type 

 colonies, and in these colonies the individual heads constitute single systems each with an apical 

 common cloacal opening, as described by Sluiter. In other, larger, heads there are up to five round 

 systems of zooids. Usually the surface of the colony is bare, but sometimes there is a coating of sand 

 or broken shell which is confined to the outer layer of the test. The test material is very clear, soft and 

 flexible. 



Zoom (Text-fig. 7B). The size and proportions of the zooid are variable, but often the thorax is 

 about 2 mm. long and the abdomen 2 or 3 mm. The post-abdomen is narrow and may be longer than 

 the thorax and abdomen combined. In some zooids the post-abdomen contains reserve material 

 (res.) similar to that often stored in the post-abdomen of other polyclinid species. 



Thorax. The oral siphon has six lobes, which are sometimes very shallow. The anterior margin of 

 the atrial siphon is elongated into a languet (a. I.) almost always provided with three narrow teeth. 

 On the posterior margin there are generally three short teeth. 



Branchial sac. Thirteen to fifteen rows of stigmata are present, each with about thirty stigmata. 



Gut. The gut is indistinguishable from that of S. adareanum, except that the stomach is not pear- 

 shaped, but this is a slight difference. The anus lies opposite the 8th row of stigmata, and is provided 

 with two lips. 



Gonads. In two of the specimens collected in December gonads are present. The ovary (ov.) is 

 small and compact, with few ova, and lies a short distance below the loop of the intestine, not, as in 

 Sluiter 's specimen, overlapping the lower part of the loop. In a few zooids there is a long series of 

 testis follicles below the ovary. 



Larva (Text-fig. 7C, D). One colony (St. 144, 5. i. 1927) had fully developed larvae in the atrial 

 cavities of the zooids. These varied from 0-54 to 0-64 mm. in length from the end of the papillae to 

 the base of the tail. In the earlier stages of development (Text-fig. 7C) the three anterior papillae 

 and the four median ampullae were seen together with a few large dorsal and ventral (lateral?) 

 ampullae. In later stages the gut and siphons could be seen and the sensory vesicle containing only 

 a spherical otolith and no trace of the ocellus. Still more advanced larvae (Text-fig. 7D) showed a 

 breaking-up of the papillae and ampullae : this stage may represent the early metamorphosis of larvae 

 retained beyond the normal period in the atrial cavity. 



Remarks. In dealing with S. adareanum I have already mentioned that S. georgianum has been 

 regarded as a synonym (van Name, 1945). Sluiter pointed out, however, in his original description, 

 that the formation of the colony in S. georgianum was different, and the colonies described above 



