PLUSTRA FOLIACEA. 115 



not be referred to a distinct group a point which can 

 only be settled after a careful study of these forms. But 

 all the British Flustridcs may be included in the present 

 genus. 



The polypide of Flustra exhibits no structural peculi- 

 arities. 



The avicularia occur in most cases under a very rudi- 

 mentary form. They are usually developed in the line 

 of the cells, from which, indeed, they differ but slightly. 

 Nowhere is the morphological significance of these curious 

 appendages more easily recognizable. 



This genus ranges to the Arctic regions and the 

 northern coasts of America (Gulf of St. Lawrence), and is 

 represented in the Mediterranean, in South Africa, in New 

 Zealand and Australia; and in China and the Society 

 Islands by F. foliacea. Of the Arctic species three (F. 

 serrulata, Busk, F. membranaceo-truncata, Smitt, and F. 

 securifrons, Pallas) occur in the Gulf of St. Lawrence ; 

 and two (F. carbasea and F. securifrons} are also British, 

 but confined to our more northerly coasts. The genus 

 has its principal seat in Europe, and is most abundant 

 and most richly represented in northern latitudes. 



a. Zooecia in two layers. 

 FLUSTRA FOLIACEA, Linnaeus. 



Plate XVI. figs. 1, 1 a, 1 b ; and Plate XIV. fig. 10. 



Po*P8 CERViifva, Jtusitu, M6ra. de 1'Acad. Boy. d. So. 1742, 290, figs. 3, A, 



B, cc. 



BROAD-LEAVED HORHWRACK, Ellis, Corall. 70, no. 2, pi. six. Bg. a, A. 

 EBCHARA FOLIACEA, Linn. Syst. ed. 10, 804 : Pallas, Klenchus, 52 : Moll, 



Esohara, Ac. 44, pi. ii. fig. 7. 

 FLUSTRA POLIACEA, Linn. 8yt. ed. 12, 1300: Ell. 4- .W. Zooph. 12. pi. ii. 



fig. 8: J'an Ben. Recherchee, 56, pi. vii. figa. 11, 17 : Larnk. 



i2 



