202 TABULATE CORALS. 



walls of no more than average thickness. Transverse sections 

 (PI. X., fig. 3) show that the walls are so entirely amalgamated 

 in contio^uous corallites that it is difficult to detect the origfinal 

 boundaries of the tubes. The same sections show that the 

 septa are in the form of strong vertical ridges, which vary 

 in number in tubes of different dimensions, but are invariably 

 marginal, and never extend beyond a very limited distance into 

 the interior of the visceral chamber. There is also no trace of 

 that division of the septa into an alternately-disposed long and 

 short series, such as has been seen to be so characteristic of 

 C. alveolata, Goldf , and C. calicina, Nich. 



Vertical sections (PI. X., fig. 3 a) exhibit principally the 

 strong, remote, and complete tabulae ; but when the plane of 

 the section comes to coincide more or less closely with the 

 plane of one of the walls of the tube, we observe also a 

 series of vertical ridges or bands, which represent the broad 

 edges of the septa as seen in section. In such parts of vertical 

 sections, I think I can detect, as before said, small mural pores, 

 but I cannot affirm this positively. 



For7natiou and Locality. — Abundant in the Trenton Lime- 

 stone of Canada and the United States. Professor Hall's 

 specimens seem to be exclusively from the Black River 

 Limestone, which forms an inferior division of the Trenton 

 Limestone in the State of New York. It has not hitherto 

 been detected in the Cincinnati formation (Hudson River 

 Group) ; and this of itself is to some extent evidence of its 

 distinctness, considering that Columnaria alveolata, Goldf. 

 {Favistella stcllata, Hall), is such a common coral in the 

 latter formation. 



