SiMi'soK — A Rci'isiim (if Ihr < Icri/iiiirlliilac .303 



XIII.— Juncella trilineata. Figs. 24-26, 

 Juncella trilineata Tliomsou and Henderson, .x.x.xix., p. 315. 



In 1905 Thomson and Henderson established this very characteristic 

 species, of whicli the following notes are of particular interest. The specimen 

 was sparingly branclied. "The polyps arise in three diflerent bands, leaving 

 three narrow, bare strips, each of which has in its centre a bare rib or keel. 

 Under each bare strip lies a large longitudinal canal." 



Only one specimen of this remarkable form has so far been described ; it 

 was obtained at Patani, Siam. 



The spicules are of the Juncella type, and are hardly distinguishable 

 from those of J. juncea. Very characteristic, however, is the presence of 

 three main canals situated symmetrically around the axis. The result of this 

 on the external appearance is that there are three longitudinal spaces on the 

 eoenenchyma devoid of polyps ; the verrucae are therefore disposed in 

 three longitudinal groups, and this arrangement is unique amongst 

 Juncellids. 



" The polyps, which measure from I'l mm. to 1'5 mm. in height, are 

 arranged in transverse rows of 3-4 ; but many smaller polyps occur which 

 break this regularity." 



For a short distance from the end of the branches the polyps occur in 

 three single rows (fig. 24) ; but passing downwards two, three, four, or more 

 are to be seen, and scattered among these are immature forms, so that all 

 that can be said with regard to the disposition of the polyps is that they 

 occur in three longitudinal groups, the exact number in a transverse row 

 depending on the position in the colony and on its stage of development. 



The eoenenchyma is of the typical Juncellid type ; it consists of an 

 outer non-canal-bearing part and an inner canal-bearing part. These are 

 separated by a concentric series of outer longitudinal canals. In the inner 

 series of longitudinal canals which separate the eoenenchyma from the axis 

 there are, however, three much larger than the rest ; these correspond to the 

 three longitudinal tracts devoid of polyps and separate off the three polyp- 

 bearing ridges (iig. 25). 



In the Indian Ocean Littoral Collection there occurs a small, simple 

 colony, 55 mm. in height and 2-5 mm. in maximum diameter. The attach- 

 ment has been broken oH', but has evidently not been far from the present 

 base. For a short distance from the base there is a portion devoid of polyps. 

 Throughout the remainder of the colony the polyps seem to be arranged in 

 three irregular longitudinal series and as a cross-section reveals what are 

 evidently the main caiials, we fool justified in referring the specimen to this 



K.I. A. FKOC, VOL. .\.\Vni., SKCT. U. [2 S] 



