97 



Fig. 49. D. harrisoni. 



braiK'lios, but it is roughly oval with its long axis coinciding with the stem. 

 One of the sides is almost fiat and has the smaller number of branches, while 

 the other side is markedly convex, with numerous branches, and an even surface 

 owing to the polyps all reaching the same level. The branches arise somewhat 

 irregularly, at times apparently in a whorl, and are almost all of equal length 

 and nearly cylindrical in the lower part ; they give 

 rise by repeated division to the polyp-bearing twigs. 

 The lower branches are smaller than the upper, 

 and in them the separation of the jjolyp- bearing 

 twigs is more complete bringing about in this man- 

 ner a more open arrangement of the polyps and 

 also a slight flattening of the upper portions of the 

 branches. 



The polyps on the upper portion are arranged 

 in large groups of somewhat angular outline and 

 concave surface. These comprise smaller groups, 

 which in their turn are composed of a number of 

 smaller bundles, in each of which there are from 

 six to fifteen polyps, which stand in close contact 

 on the short stalks of 0'5 mm. in average length. 

 On the lower branches they stand more openly, 

 but are still arranged in small groups. They are small and rounded in shape, 

 about 048 mm. in height and in width. They are placed at an obtuse angle on 

 the stalk and have their spicules arranged in eight double rows. In the lateral 

 and ventral double rows there are four pairs of converging spicules, in the 

 dorsal there are three to four pairs. Of these the ui)permost pair is slightly 

 larger than the others, but as a rule does not project. The polyp-spicules are 

 spindles, averaging about 0'24 mm. in length and bearing a few simple spines. 



The Stiitzbiindel is well developed, and usually two spicules project beyond 

 the polyp. These spicules may reach a length of 1-8 mm. and project for a 

 distance of 0'42 mm. beyond the polyp, but the average is considerably less. 



Cortical spicules : («) In the stem the spicules are spindles either straight 

 or curved, and covered with simple, blunt, regularly arranged spines. They 

 often show a bifurcation at the end, and average in the smaller groups about 

 0*4 mm. and in the larger about 2'2 mm. On the stem they are arranged more 

 or less transversely, and in the branches and twigs nearly longitudinally. 



(//) In the stalk there are short, thick spindles, clubs, three-rayed and 



numerous flattened and irregular forms. All have numerous prominent branched 



spines except the flat irregular forms and flat spindles which have rough warts. 



The spindles measure about I'l mm. in length and 0'24 mm. in breadth, but 



there are numerous forms which vary from 0-25 to 09 mm. in length and from 

 13 



