1 78 JV. I. Robinson, 



Other Peculiar Forms Sometimes Called Hexacoralla. 



As recent work has emphasized the importance of a six-septal 

 stage in the life history of a tetracoral it is not surprising to find 

 a few species belonging to that sub-class which have only six 

 septa in adult forms. 



Battersbyia gemmans from the Devonian of England is excep- 

 tional in that some of its buds have six septa while others have 

 a larger number. According to Neumayr (1889 B), the normal 

 calices bear numerous buds on their borders. A part of these 

 buds undergo a process of development like that of the parent; 

 another part never develop more than five or six septa and within 

 these smaller corallites several new ones form by "septal bud-; 

 ding," a process which suggests that of fission. The products^ 

 of the six-septal individuals, curiously, develop into ordinary 

 large corallites with many septa, and like them produce huds at 

 their borders. Specimens of this species have not been available, 

 but judging from the illustration (Neumayr 1889 B: 276), there 

 is nothing to suggest a close relationship with Hexacoralla. 



Hexaphyllia. — The genus HexaphylUa from the Lower Car- 

 boniferous of Europe has also been listed with Hexacoralla. 

 The corallites are long, slender, and prismatic and have but few 

 septa. There is some doubt as to the limits of this genus. Forms 

 agreeing with the original description were once included in 

 the genus Heterophyllia, a group which Neumayr (1889 B) 

 considered to be dimorphic, producing corallites with many septa 

 as well as others with only six in much the same way as in 

 Battersbyia; but Duncan (1867:644) in redefining the genus 

 Heterophyllia concluded that the small individuals belong to 

 another and distinct species. 



A. Stuckenberg (1904) found specimens of the small six- 

 septal forms in Russia at the village Ploskaja on the left bank 

 of the river Pronja. For these he made a new genus Hexaphyl- 

 lia, basing it upon the single species H. prismatica defined at the 

 same time. As the genus now stands it contains also H. m'coyl 

 (Dimcan), H. lyelli (Duncan) and H. mirabilis (Duncan), 

 species formerly included in the genus Heterophyllia. 



Heterophyllia. — Specimens of Heterophyllia cf. sedgwicki 

 Duncan from the Scottish Lower Limestone Group (Lower 

 Carboniferous), Dunfermline, Scotland, give clear evidence that 

 this genus follows the law of septal addition which is characteris- 



