76 " ENDEAVOUR " SCIENTIFIC RESULTS. 



MOPSEA PLUMACEA, Sp. 710V. 



(Plate iv., fig. 1 ; Plate vii.) 



This new species is well represented by several complete 

 colonies, and a number of incomplete branching pieces. 



One complete specimen is 22-5cm. in height, with a maxi- 

 mum breadth across the expanded portion of 11cm. The 

 colonies are typically feather-like, the long frond-like 

 branches bearing on each side a row of alternating twigs. 

 These twigs usually remain simple, but occasionally branch 

 in the same pinnate manner. The colony is attached by a 

 well developed calcareous expansion, about 12mm. in thick- 

 ness. From this there rises a cylindrical stem, 2-5mm in 

 diameter. At a height of 5- 7cm., the stem divides into two 

 main branches, which bear numerous twigs. The branches 

 have a diameter of 2mm. Branching is confined to one 

 plane. 



The axis is composed of white calcareous internodes with 

 fine longitudinal fluting, and short amber-coloured nodes. 

 The longitudinal ridges of the calcareous joints are dentate. 

 Near the base of the stem, the horny nodes have lengths of 

 2-3mm., and the calcareous internodes of 0-5mm. In 

 some cases the internodes are entirely overlapped by the 

 horny joints. Higher up the calcareous joints are l-5mm. in 

 length, the horn}^ joints being reduced to 0-25mm. The 

 calcareous internodes give rise to one twig each in alternate 

 succession. 



The coenenchyma is thin, and on the twigs is almost en- 

 tirely hidden by the numerous polyps. These occur in 

 close- wound spirals over the whole surface of the twigs. In 

 the youngest twigs the spiral is wider, but nowhere is there 

 any trace of a bilateral arrangement. On the branches, 

 however, a few scattered polyps occupy a lateral position, 

 here and there encroaching on the middle line. 



The polyps are small, 0-5-0-75mm. in height, and club- 

 shaped, with truncate mouths, which turn upward toward 

 the extremity of the twig. In several instances inverted 

 polyps were observed with their mouths directed towards 

 the proximal end of the twig. The calyces are armoured 

 with longitudinal rows of transversely arranged, shghtly 

 overlapping scales ; there are from ten to twelve of these in 

 the abaxial rows. These spicules are arranged in an imbri- 

 cate manner ; the imbrication being clearly seen in a profile 

 view of the polyp. 



