244 SERTULARIIDJE. 



Genus DIPHASIA, Agassiz. 



SERTULARIA (auct.) (in part). 

 BYNAMENA, Lamouroux (in part). 



GENERIC CHARACTER. Zoophyte plant-like ; stem more 

 or less branching, jointed, rooted by a creeping stolon; hy- 

 drothecte opposite, a pair on each internode, occasionally 

 subalternate, with an internal, valve-like operculum ; gono- 

 thecas scattered, differently shaped in the two sexes the 

 female ample, more or less cleft or divided into segments 

 above, containing a marsupial chamber ; the male smaller, 

 with a central tubulous aperture. 



OF this beautiful genus D. rosacea may be taken as the 

 type; it strikingly represents the characteristics of the 

 group. Diphasia agrees generally with one section of the 

 genus Sertularia in the arrangement of its calycles ; but 

 they are furnished with a plain or rarely an obscurely 

 toothed aperture, while in the latter they are decidedly 

 bilabiate or rnucronate. But the chief distinction is 

 found in the structure of the reproductive capsules, which 

 exhibit great uniformity throughout the genus, and differ 

 essentially from those of the allied groups. 



In all the species of Diphasia the female gonotheca 

 encloses a more or less spherical chamber or marsupium, 

 which surmounts the axial column, and into which the 

 contents of the several sporosacs are successively dis- 

 charged (Plate XLVIII. fig. 1, d) . The uppermost portion 

 of the capsule, immediately surrounding this chamber, is 

 always cleft or divided into segments, either free or slightly 

 adherent, which open for the passage of the planules when 

 mature. The external form varies in the different species ; 

 but these points of structure are constant. 



The male gonotheca exhibits universally the same general 

 figure. It is usually much smaller than the female, and 



