BICELLARIIDJE. 



65 



Fig. 2. 



In the latter the tubular portion of the cell towards the 

 base is reduced in length, and the aperture occupies fully 

 two thirds of the front ; occasionally (as in B. umbella, 

 Smitt) it extends to the bottom. 



These two genera are united through the species of 

 BiceUaria in which the aperture encroaches most upon 

 the tubular base of the cell, and the species of Bugula in 

 which it is most contracted. 



In such forms as B. Murray ana, with its elongate, boat- 

 shaped cell, open in front through a great 

 portion of its length, and margined with 

 spines (woodcut, fig. 2), or B. umbella, 

 with aperture actually extending to the 

 base, we have a near approach to the 

 form of Diachoris, which may be described 

 popularly as a Bugula with its cells dis- 

 joined and held in connexion by a num- 

 ber of tubular processes, and assuming a 

 decumbent instead of an erect habit of growth. These 

 two genera also agree in having capitate avicularia of 

 much the same type, and occupying similar 

 positions in the zoarium. It is only in 

 this family that we meet with the capitate 

 and jointed avicularium the true " bird's 

 head," with its elaborate structure and 

 curious movements, the most highly spe- 

 cialized form which the organ assumes. 

 In Beania we have a form closely allied to 

 both Bugula and Diachoris. The latter 

 is distinguished from it by the more com- 

 plex character of its zoarium, and by the 

 presence of avicularia. There is little dif- 

 ference in the habit of growth ; for in some 

 species of Diachoris the cells are semi- 



Bugula Murrayana. 



Fig. 3. 



