septa either unite by a few trabeculae or join across the axial 

 space." In Flahellum there is no columella, but the septal edges 

 unite by trabeculae in absolutely the same way. In F. ruhriim 

 there is often very little such fusion of the septal edges, indeed not 

 more than is found in some specimens of i?. fragilis Pourtales 

 and R. tulipa Pourtales. In R. typiis Ed. & H., R. oj^ms 

 Duncan and R. levidensis Gardiner there is no such fusion, 

 but the above species of Pourtales are in this respect inter- 

 mediate. Ed. h H. remark that in R. typus the larger septa 

 have in the young traces of trabeculae, which disappear in 

 the adult. How far the presence or absence of a false 

 columella can be regarded at all as a generic character is 

 doubtful, but certainly in this case there is no valid reason 

 for separating RhizotrocJnis from Flabclhim. 



The characters of the genus Flabelliu/iwoviXd be practically 

 synonymous with those of the alliance Flabelloida, as given 

 above, and hence need not be repeated. 



The chief distinguishing characters of species within the 

 genus i^/«<5<?//«?y/ appear to be ( I ) shape as seen in side view 

 and looking into the calicle as well as in transverse sections of 

 the calicle : (2) if the corallum be free, whether there has 

 been a distinct rupture of the stalk, leaving a scar or not : (3) 

 the number of septa fusing together by their septal edges or 

 the number of equal septa of the lowest cycles : (4) if com- 

 pressed, the presence or absence of wings or hollow epithecal 

 processes, or possibly both, or if round, the presence or 

 absence of root-like processes. As Semper has shown, and 

 as will be subsequently seen in F. ruhrum^ (3) and (4) may 

 require a large number of specimens to ascertain definitely 

 these characters, but in some forms they become of primary 

 importance (those cited above formerly placed in genus 

 Rhizotrochus and others). (2) appears to be correlated with 

 changes of shape, (i) varies considerably in any species, but 

 the vast majority of specimens in each species approach to a 

 distinct, central type. The shape within the genus varies 

 greatly, some species being compressed, others round or 

 angular. In some species the epitheca, as a flat plate, joins 

 the outer edges of the septa and in others forms festoons 

 between the same. In some the upper edge of the epitheca 

 follows regular curves, the septa all attaining the same 

 height, and in others is quite irregular, some cycles of septa 

 rising higher than others. 



Of supplementary characters the septal contours depend 

 largely on the shape of the corallite, but the distances between 

 the spined ridges on the septal sides may be of some im- 

 portance. The latter vary somewhat in individuals of 

 presumably the same age — judging by their accretion-lines — 

 and of similar size and shape. Much more then do they vary 



