DESCRIPTION OF SPECIES 41 



to a ridge which extends on each side along the dorsal and ventral parts of the trunk. This arrangement 

 is like that described by Carlisle (1952) in Polyclinum aurantium Milne Edwards. 



The only colonies in the collection with larvae were two taken in March (St. 190); all the larvae 

 from one colony have both ocellus and otolith (Text-fig. 5E), but all those from the other colony 

 lack an ocellus. This is a very curious fact, but as the larvae and the zooids from which they come are 

 identical in all other respects, I cannot doubt that both colonies are of A. caeruleum. 



According to Sluiter (1906) and Kott (1954) the larvae are contained in a brood pouch, but Hart- 

 meyer (191 1) doubted the existence of a special pouch. In the ' Discovery ' specimens the larvae were 

 lying in the atrial cavity, as they normally do in species of Aplidium. 



Biology. It is not possible to add anything regarding the general biology of the species from the 

 scanty material available. Hartmeyer (191 1), however, from a study of his rich material, found all 

 stages of male and female ripeness at all seasons, the larvae not being confined to any one period. They 

 were present, for instance, both in January and in July. This is a remarkable case of independence 

 of temperature in the breeding cycle of an antarctic ascidian. 



Remarks. The identification of the specimens in the collection is not in doubt, except the single 

 colony from Marion Island (St. 1563). In this colony all the zooids are degenerate and identification 

 rests on the shape and texture of the colony, which closely agree with typical colonies of the species. 

 There must remain considerable doubt, however, especially in view of the more northern latitude of 

 the station. 



Distribution. Western Antarctic (Graham Land, South Shetlands), Eastern Antarctic (Kaiser 

 Wilhelm II Land, MacRobertson Land, Enderby Land). (PMarion Island.) 



Aplidium stanleyi sp.n. (Text-fig. 6 A, B, C) 



Diagnosis of species. Colony consisting of low heads arising from a sandy base. Zooids with the 

 atrial opening a little way back along the dorsal side of the thorax. Twelve to fifteen rows of stigmata. 

 Post-abdomen narrow, even with fully developed gonads. Stomach with twenty to twenty-four 

 longitudinal folds. Testis a long series of small follicles. 



Occurrence. St. WS 229: Falkland Islands, 210-271 m. 



Holotype. St. WS 229: size — 12 mm. wide at base, 11 mm. high. 



Colony (Text-fig. 6 A). This species is represented by many colonies taken in a single haul from 

 the continental shelf round the Falkland Islands. The largest colony is 1-4 cm. high and 1-4 cm. wide. 

 Typically each colony consists of one head or a few heads joined basally, where there is an expansion 

 of the common test which is here heavily impregnated with sand. At its junction with this base, the 

 head is narrowed and the upper part is expanded with a rather flattened or slightly dome-shaped 

 apical end. The test material is sufficiently clear to allow the zooids to show through. They are 

 arranged in a single system in each head, no head having been found with more than one common 

 cloacal opening. The basal sandy test is often produced into a number of finger-like processes or 

 broad lobes, and the colonies appear to have been loosely attached to the sandy substratum. 



Zoom (Text-fig. 6B). The zooids are small, averaging about 5 mm. in length, of which the thorax 

 and abdomen account for about 2 mm. 



Thorax. The oral siphon has six pointed lobes. The atrial opening is placed a short distance back 

 along the dorsal side of the thorax, opposite to the 3rd row of stigmata, and is a simple round hole, 

 bearing on its dorsal margin a languet («./.). The languet is sometimes simple and triangular, but more 

 often is divided into a long narrow median lobe and a short pointed lobe at its base on each side. The 

 muscles on the thorax are only moderately well developed. There are from twelve to fifteen rows of 

 stigmata in the branchial sac, each row with about fifteen stigmata. 



