BRITISH ZOOPHYTES. 227 



appendage are in keeping with its curious structure. 

 The whole head ordinarily sways to and fro upon the 

 slender joint at the poll^ at intervals of a few seconds ; 

 but besides this motion, which is even, though rather 

 quick, the lower mandible, which commonly gapes to 

 its utmost extent, now and then, at irregular intervals, 

 closes with a strong sudden snap, much like the 

 snapping of a turtle's jaws, and presently opens again 

 and leisurely resumes its former expansion." 



2. B. Alderi, Busli. 



B. unispinosa (Sars). 



Hab. : Shetland, Hebrides {A. M. N.). ' 



This species is white in colour, and branches dicho- 

 tomously. It is considered by Mr. Hincks to be a 

 transition species between the uniserial and biserial 

 forms, as the zooecia, although side by side, are not 

 united throughout their whole length. Each cell is 

 armed with a single long curved spine. " The ovicells 

 remind one in their form of the flower of the calceo- 

 laria, to the form of which they bear a close resem- 

 blance." — Norman. 



Genus II. Bugula, OJien. 



Zoarium erect, phytoid. Zooecia boat-shaped, or 

 subquadrangular, elongate, united in two or more 

 series. Aperture occupying a large proportion (occa- 

 sionally the whole) of the front, not turned upwards or 

 oblique. Avicularia in the form of a bird's head, 

 pedunculate and jointed, usually one in each cell. — 

 T. H. 



1. B. AvicuLAEiA, Linn. Plate XVIII. fig. 1. 



Sertularia avicularia {Linn., Ttirt., Berk.), Cellaria 

 avicularia {E. and S., LamJc., G. J.), Crisia avicularia 



Q 2 



