CHORIZOPORA. 223 



diately from cell to cell ; and the zooecia have then 

 the appearance of being surrounded by a single line of 

 punctures; in other cases a number of tubercles are 

 interposed between the cells^ which are connected with 

 one another and with the neighbouring zooecia by tubular 

 bands ; and in this way a reticulated crust is formed, 

 which is often of considerable extent. The tubercles, 

 which are really modified cells, are sometimes merely per- 

 forated at the top ; but they frequently bear avicularia : 

 one o£ them is always placed (in C. Brongniartii) at the 

 upper extremity of the zooecium, or on the summit of the 

 ovicell, when present. 



The only species, I believe, which is referable to this 

 genus is the Flustra Brongniartii of Audouin. Its affi- 

 nities are somewhat obscure ; but the simple semi- 

 circular orifice allies it to the present family, while the 

 absence o£ the special pore and the peculiar condition of 

 the zoarium seem to entitle it to a separate place. 



The mode in which the cells are developed in C. Brong- 

 niartii, though by no means unique, differs from that 

 which is prevalent in this section of the Polyzoa. In the 

 incrusting forms, massed together under the old genus 

 Lepralia, we usually find that the nascent cells on the 

 edge of the colony are sketched out to begin with ; they 

 are outlined in full ; the foundations of the whole structure 

 are first laid, and on these the walls are gradually built up. 

 But in C. Brongniartii (and some other forms) the cell 

 growls upwards from the base, each section of it is com- 

 pleted at once; there is no ground-plan of the whole. 

 Increase takes place along the free upper extremity; and 

 the successive increments are marked by transverse strise 

 on the surface. 



The same mode of growth occurs in Schizoporella 

 hyalina. 



