64 SHELL GALLEKY. 



tions on bladder-wrack, which, owing to their flexibility, are able to 

 adapt themselves to the swaying of the fronds of the Fucus. 



The Selenariidae (Case B 2) form free colonies, usually orbicular 

 in shape, convex above and concave below. In Lunulites capidus 

 alternating rows of cells and vibracula radiate from the centre of 

 the colony. 



Section G. Eschaeina. — In this group, the front walls of the cells 

 are wholly calcareous. Many species form patches or crusts on shells 

 etc., and hence the name of the section ; other species, again, form 

 stony tree-like growths, or thick plates. Frequently one and the 

 same species occurs in the form of crusts or of erect lamellae, the 

 identity being recognised by the characters of the individual cells. 



Often a large number of species may be found on one shell. 

 Two good examples of this are exhibited in Case A 2. 

 Case A 2. Lepralia pallasiana (Fig. 13) forms sub-circular vitreous patches 



on stones and shells ; the cells are rather large, broadly oval, and 



Fig. 13. 





!•> 



A B 



Lepralia pallasiana, incrusting a shell. A, natural size ; B, cells magnified. 



with the front wall punctured with pores ; the aperture is squarish 

 and with a slight indentation on each side. 



Lepralia foliacea forms a massive coral-like growth composed of 

 thin contorted plates which fuse to form labyrinthine cavities, the 

 plates being constructed of a double layer of cells back to back. A 

 large specimen from the English Channel is exhibited in Case B, 

 upright part. In Lepralia the orifice and lid of the cell have a 

 straight lower margin, but one large group, Myriozoidce, is characterised 



