INVERTEBRATE ANIMALS. 11 



Family ASTR^IDiE. a<Trpov, a star. 

 Group 30.— Division ASTR^EACE^ (Milne Edwards) 

 and allies. The species of this group are amongst 

 the most important of reef-building corals. Estimated 

 number of species : recent, 122 ; 'British, ; fossil, 

 267. Mesozoic and Kainozoic. 



IT Heliastj'cea, Acanthast7'(sa, Astrcea, Prionastraa, 

 Isastrcea, Culicia, &c. 



Group 31.— Section LITHOPHYLLIACE^ MEANDRO- 



IDM (Milne Edwards). Estimated number of species: 



recent, 69 ; British, ; fossil, 34 ; chiefly Kainozoic. 



IT Brain Corals. The polype-cells form long sinuous 



channels like the windings of a stream, or the 



convolutions of the brain ; hence the familiar 



name. 



In the Lettuce Coral, the cell-walls are as thin as 



paper, the polypes large and beautifully coloured . 



Upper Compartment. 



Meandrina mammosa, called by sailors Neptune's 

 Shield ; and other large corals. 



Group 32.— Sections LITHOPHYLLIACEiE CESPITOS^ 

 et SIMPLICES (Milne Edwards). Estimated num- 

 ber of species : recent, 30 ; British, ; fossil, 154. 

 From the Trias upwards. In genus Mussa (Oken), as in 

 Astrcea and Meandrina, the corals grow in hemispheres 

 attaining ten or twelve feet in diameter, adorning the 

 ocean bed with richly coloured cupolas. 



H Examples of nearly all the recent genera. 



