686 " THBTIS " SCIENTIFIC RESULTS. 



PLUMARELLA FILICOIDES, sp.nov. 

 (Plate Ixv., fig. 5 ; pi. Ixviii., fig. 1 ; pi. Ixxviii.) 



Stations 13, 17, 34, 48. 



■ Several colonies, each a single fern-like frond, the largest 

 23 cm. in height. From a slightly encrusting base rises the 

 ■ cylindrical stem — 3-5 mm. in diameter — which, from a point about 

 2 cm. above the base bears a single row of twigs along each side,, 

 the twigs on one side alternating with those on the other. The 

 average length of these twigs is 4 cm. and their diameter 2 mm. 

 They are rather distant, there being about twelve on each side 

 in a stretch of 5 cm. In a few cases a stouter branch is given 

 off from near the summit of the colony, bearing in its turn lesser 

 twigs in a single row on each side. 



The whole surface of the twigs is covered with a close- wound 

 spiral of polyps ; on the stem the polyp-arrangement is bilateral, 

 though here and there a few encroach on the middle line. 



The polyps show distinct dimorphism. The majority are very 

 small (-5 mm. long), and inconspicuous, being partially sunk in 

 the ccenenchyma, and pressed against the branch. They are 

 armoured with a few broad scales ; in the abaxials, which are 

 the most complete of the longitudinal rows, there are from three 

 to four scales ; the adaxials are practically absent. The oper- 

 culum is a sharp cone, formed of eight rather high isosceles 

 triangles. 



Here and there among the smaller polyps there are large polyps 

 of about twice the size. These are pressed against the branch, 

 but are so swollen out with reproductive bodies that they project 

 as large, rounded warts. Not only in size do these larger polyps 

 differ from the others ; they have a much lower operculum, and 

 their armature consists of a larger number of scales — there are 

 usually four scales in the abaxial rows and two to three in 

 the adaxial-laterals. The polyp-scales are broad and heavy, 

 approximately fan-shaped, and closely studded with tuberculate 

 warts; the clear border of the scale is very narrow, and bears 

 well-marked ridges. The following measurements were taken of 

 length and breadth in millimetres : — "476 x -357; -391 x *204 ; 

 •391 X '51 ; -289 x '272. The opercular scales have dimensions 

 of -391 X •204 mm.; ^323 x •204 mm. They are marked with a 

 strong T-square ridge ; the clear border is relatively broad and 

 smooth. 



The ccenenchyma is covered with a close mail of rather large 

 scales, similar to those on the polyps, but with the clear border 

 either very narrow or entirely obsolete. The following measure- 



