TABULATE CORALS. 



sions, each composed of a single layer of corallites, these layers 

 frequently anastomosing and uniting with one another (fig. 9, 

 a and b). Between each pair of corallites, and forming the 

 medium of junction between their opposed faces, is generally 

 a much smaller tabulate tube, with close-set tabula; (fig. 9, d). 



■ a ^^Sf* 



Fig. 9. — «, Halysites catcjiiilarla^ Linn., small variety, of the natural size ; /', Large variety of 

 the same, of the natural size ; c, Halysites agglomei-ata. Hall; d. Section of two corallites 

 of the same, enlarged. Niagara Limestone. 



The larger tubes are crossed by complete, generally horizontal 

 tabulae, which are much farther apart than those in the smaller 

 intermediate tubes. The septa are minute and spiniform, and 

 the walls of the corallites are entirely compact and imperforate, 

 nor are there any connecting- tubes by which the visceral 

 chambers of different polypes are placed in communication. 



By Milne-Edwards and Haime the family of the Halysitidcz 

 was made to include the SyringoporcB ; and that there are cer- 

 tain alliances between these groups cannot be denied. I con- 

 sider, however, that the fact that the polypes of Halysites are 

 destitute of any communication with their neighbours is suffi- 

 cient of itself to warrant the separation of the genus from the 

 Sy7'ingoporidcB. The latter, as has been seen, may perhaps 

 be regarded as aberrant Perforate Corals ; but it is difficult to 

 speak at all positively as to the systematic position and aftin- 



