Dr. J. E. Crray on a new Genus q/" Eschariclae. 167 



XXIV, — On Flustra marginata of Krauss and an allied 

 Species, forminq a new Genus (Fliistramorplia) o/'Escharidse, 

 from Natal. By Dr. J. E. Gray, F.K.S. &c. 



In the collection of corallines containing a few seaweeds, 

 especially the one described in the August number of the 

 ' Annals,' received some years ago from Port Natal as a pre- 

 sent from Colonel Bolton, I observe several specimens of the 

 Flustra marginata described by Dr. Krauss in his ' Corallines 

 and Zoophytes of the South Sea,' p. 'db, tab. 1. fig. 3. The 

 figure of this coralline has always been a matter of curiosity 

 to me ; and therefore it was with great pleasure that I found 

 several specimens of this and an allied species in the collection. 

 Their formations are very peculiar, having the frond-like 

 form of a Flustra, but supported by horny, often inosculating 

 fibres, that margin the frond and also traverse it in various 

 directions so as to break it into several sections, as is well 

 represented in Krauss's figure. One might be inclined, as 

 it often grows among the dead denuded stems of zoophytes, 

 to believe that those zoophytes formed the margin of the frond ; 

 but a study of numerous specimens has convinced me that this 

 cannot be the case ; for the thickened horny margins do not 

 stand out from the ends of the fronds, as they would do if they 

 were the denuded stems of other species, but they are evidently 

 developed on the edge and across the frond as the frond grows. 



The substance of the coral is calcareous and exactly like 

 those of Lejyralia and Eschara ; and it forms a frond with a 

 series of cells on each side like the latter genus. The fronds 

 are expanded, repeatedly and furcately branched like the com- 

 mon Flustra, but they are known from that genus by the cells 

 being much more calcareous and covered with a calcareous 

 coat. The two species have a general external resemblance 

 to the two common European Flustras F.foliacea and F. trun- 

 cata ; I therefore propose to call the genus Fliistramorplia. 



Krauss, when describing Flustra marginata, observes that 

 "perhaps it may become the type of a separate genus on account 

 of the thickened edges, which, standing out from the calcareous 

 structure, border the two margins of the frond. Where the 

 frond divides, the thickened edge of the upper margin tui'ns 

 across it ; and consequently it appears that the growth of the 

 branch is continuous ; but here a pause occurs, during which the 

 thickened margin is forming, which after a time constitutes the 

 foundation of a new lobe. These cross lines show the different 

 epochs of growth, like the varices on Murices and Cassidce 

 and other genera of shells. 



" These thickened ribs give the strength and firmness which 



