72 ' ENDEAVOUR " SCIENTIFIC RESULTS. 



MOPSEA AUSTRALIS, Thomson and Mackinnon. 

 (Plate vi.) 



Mopsea australis, Thomson and Mackinnon, Mem. Austr. 

 Mus., iv., 13, 1911, p. 675, pi. Lxiv., figs. 1, 2, pi. 

 Ixvii., fig. 5. 



A solitary but magnificent lyre-shaped colony represents 

 this species, which was described by Thomson and Mackinnon 

 from very fragmentary specimens. 1 It is 37 - 5crn. high, and 

 consists of a main stem, 4 mm. in diameter, which arises 

 from an encrusting, disc-like, calcareous base. The colony 

 is expanded in one plane, and has a width of 20cm. in its 

 widest part. At 3-2cm. from the base the main stem divides 

 into two ecjual branches. These primary branches give off. 

 along the upper side alone, a series of parallel ascending 

 secondary branches, which soon attain to nearly the same 

 thickness as the main branches. In this manner there arises 

 the appearance of a continuous dichotomy. At the same 

 time the main branch tends to bend outwards after each 

 secondary branch is given off, so that its course describes a 

 series of shallow curves. The secondary branches either 

 divide dichotomously or remain simple throughout their 

 length. In general appearance and mode of branching the 

 colony is very similar to Mopsea dichotoma (Linnaeus). 



The coenenchyma is thin, and where it has been worn off. 

 the axis shows the usual white calcareous internodes with 

 well marked longitudinal fluting, and the short brown- 

 coloured nodes. 



The polyps are club-shaped, and occur in close spirals 

 round the branches, to which they are very closely pressed, 

 so that their mouths are hidden. 



The spicules include the following forms : (1) elongate 

 to oval scales, with large teeth round their edges, and a few 

 warts scattered over the surface -192 x -087mm. ; -183 x 

 105mm. ; -157 x 087mm. ; -122 x -070mm. ; (2) warty 

 spindles and clubs -157 x -035mm. ; -122 x -017mm. ; -105 

 x -035mm. ; (3) Capstans, a few crosses, and small irregular 

 bodies -070 x -035mm. ; -052 x -035mm.; -052 x -052mm. ; 

 052 x -017mm. 



1. I heave not been able to find, among the specimens returned to the 

 Australian Museum by Thomson and Mackinnon, any specimen labelled 

 as the type of Mopsea australis. I conclude, therefore, that it must have 

 broken up. The co-type, consisting of a number of " branching pieces of 

 various lengths " has been preserved. 



