ON THE BBITISH SPECIES OF CRISTA. 143 



(C. eburnea) on a colony which, from the presence of spines 

 or from other characters, was found to belong to C, aculeata. 

 I cannot admit that there is sufficient evidence to show 

 that this form is merely a variety of C. eburnea. Both 

 in the form of its zocecia and in its method of branching 

 it is totally unlike this form, although it is sometimes with 

 difficulty distinguished from C. ramosa. 



The branches of C. aculeata are usually slightly incurved, 

 but not nearly to the same extent as in C. eburnea; and it 

 does not possess the well-developed helicoid cymes of the 

 latter species. Many of the internodes bear two branches, 

 usually on opposite sides, but more rarely on the same side. 

 In well-developed colonies the terminal internodes, and espe- 

 cially those which possess ovicells, are commonly provided 

 with two branches. 



The number of zocecia in an internode is extremely variable j 

 it is usually small in the lower internodes of a stem, such 

 numbers as 1, 3, 3, and 4 being common in this position. The 

 next parts of the stem, and the basal parts of the lateral 

 branches given off by it often assume an eburnea-like appear- 

 ance, the internodes consisting of 5 or 7 zocecia. At the ends 

 of well-developed branches the number usually becomes 

 higher ; a terminal internode with 33 zocecia has been observed, 

 although this number is higher than is usually the case. 

 When the terminal internodes have many zocecia they usually 

 bear two branches ; but if the number of zocecia is still larger 

 the number of branches may increase to as many as five. 



The position of the branches is another very variable 

 feature. In the lower parts of a colony the branching takes 

 place commonly from ^^ ; while higher up, although some of 

 the branches still come off from z-^^, others are given off quite as 

 commonly from z^, and in many of these cases the zooecium 

 below the branch, and on the same side, bears a spine. 

 Branching may, however, take place from the higher zooecia of 

 an internode, as from z^ or z^; and when several branches 

 come off from the same internode, those which are last 

 formed have a very high position in the internode. The 



