46 



Dendronephthya thuja, Henderson. 



This species is represented by a rigid bush-shaped colony which measures 

 about 5 cm. in height and 3 cm. in greatest breadth. 



The stalk is thick and rigid, measuring about 2 cm. in length. It is 



granular in appearance and has a broad base of 

 attachment, with no trace of stolons. 



The polyparium is irregularly cylindrical in 

 shape with a strong development of the branches 

 all round except on one side, where there are 

 very few branches. The stem rises entire, giving 

 off branches of various sizes all round, which by 

 their repeated divisions give rise to the polyp- 

 bearing twigs. The two lowest branches are 

 flattened, the larger being leaf-like and almost 

 surrounding the stem, leaving only a small free 

 space between its edges in which the second 

 branch arises, the latter having a cylindrical lower 

 portion and a flattened concave upper portion. 

 From the upper surface of the flattened, leaf-like 

 branch, small ordinary branches are given off. 

 The leaf-like branch is also reflexed and thus 

 forms a collar to the upper portion of the stalk. 

 The polyps are arranged in small groups of four to eight, and on the edge 

 of the flattened branches they may occur singly or in small groups. They are 

 small, roundish, and measure on an average 04 mm. in height and 0'4 mm. in 

 breadth. The polyp-spicules are arranged in eight double rows of four pairs 

 of converging spicules each, the uppermost pair being slightly larger and pro- 

 jecting a little beyond the polyp. The lower polyp-spicules average about 0-24 

 mm. in length, the upper about 0"4 mm. On the aboral surface of each tentacle 

 there are two rows of small flat, rod-like spicules. 



The Stiitzbiindel consists of a number of spindles of about 0'9 mm. in 

 average length which converge to a point and scarcely i)roject beyond the 

 polyp. 



Cortical spicules : (a) In the stem there are thick spindles with numerous 

 multituberculate warts and smaller slender spicules with few spine-like protu- 

 berances. The larger spindles average about 2") mm. in length and vary from 

 0-0(J to 048 mm. in breadth. 



{h) In the stalk the spicules are similar to those of the stem cortex but 

 slightly smaller, and there are in addition clubs, oval-shaped discs and irregu- 

 larly branched forms. 



Fig. 25. D. thuja. 



