136 SIDNEY F. HAEMBE. 



The calcareous matter of the ectocyst is considerably thicker 

 in C. denticulata than in any of the other British species. 



C. eburnea. Fig. 6. 



Although this species is not likely to be mistaken for C. 

 denticulata^ T believe that it is more nearly allied to that 

 species than are any of the other British forms. This is shown 

 by the flatness of the iaternodes, by the fact that each inter- 

 node has normally one branch, and by the characters of the 

 apertures of the zooecia. 



The branching may be illustrated by the formula^ — 



=(5+if)+ ! 



i=(5+»-i) + 



i=(5+:^)+ I 



'=(5+»-i) + 

 '=(5 + 1^)+ I 



I l=(4+a:) 



'=(3+^) 

 — representing the partial formula of a branch of a colony found 

 in April, in which ovicells were very numerous. The ovicell- 

 bearing internode on the right side of the formula is the one 

 which has been represented in PI. XI, fig. 6. 



The tendency of the branches of this species to arrange 

 themselves as unilateral sympodes is here most marked ; and 

 the formation of these helicoid cymes — again borrowing a 

 botanical term — is one of the most characteristic features of 

 C. eburnea. This was recognised by Johnston,^ who says of 

 this species, " Polypidom much branched, the primary divisions 

 alternate, spreading j the secondary from one side only." It 

 will further be noticed that in parts of a colony in which this 



' See explanation of this graphic method given on p. 146. 

 = ' Brit. Zoophytes,' ed. 2, p. 384. 



