CORALLUM OF TURBINARIA. 363. 
Mr. Bernard has termed the “ bifrontal” type of growth, the 
elevated folds become greatly extended and their apposed lower 
surfaces fuse together all over: a corallum may thus arise which 
consists of numerous close-set vertical plates bearing polyps: 
upon each of their faces and connected with each other by but a 
shght attachment at their bases. The narrow, more or less 
radial, interspaces of this type are practically open all round 
and so afford no lodgement for silt*. In Bernard’s ‘“foliate”” 
and “ mesenteriform ” types the elevated folds, instead of fusing 
together back to back, persist either as open frills, or, meeting, 
fuse only along the lines of junction. In this way a corallum. 
consisting of a series of connected cylinders or cups, open at 
their bases, and bearing polyps alternately upon their inner and 
outer faces, may arise. By the suppression of the elevated folds 
a series of cups, each having, like the parent cup, an internal. 
polyp-bearing surface, may be formed; while an exceedingly 
interesting extension of this type of growth is afforded by those 
eases in which the growth of the depressed folds has been. 
arrested, so that the corallum has come to consist of a series of. 
Figs. 11-14. Diagrams to show the origin of various types of growth by the: 
folding of the margin of the primitive cup or disc. The polyp- 
bearing surfaces are dotted. 
* A series of specimens well illustrating this type is figured by Mr, Bernard 
as T. gracilis, Brit. Mus. Catal., pl. xxiii. 
