ixo TABULATE CORALS. 



all ; and the calices now appear as if sunk in a dense coenen- 

 chyma, superficially adorned with discontinuous striae (PI. V., 

 fig. 4 a). Moreover, a careful microscopic examination shows 

 that this dense interstitial tissue is, in parts at any rate, ren- 

 dered minutely porous by the presence of numerous excessively 

 small cavities. 



The general appearances presented by this species — as 

 apparently also by the type-species T. Davidsoni, E. and H. — 

 are entirely such as would support the view entertained by 

 Milne- Edwards and Haime — namely, that we have to deal 

 in Trackypora with composite corals, the corallites of which 

 are sunk in a general coenenchyma. Thin sections, however, 

 render it abundantly clear that this is not the case, but that the 

 thickened interstitial tissue between the actual tubes of the 

 corallites is only due to the deposition of delicate concentric 

 laminae of sclerenchyma round the visceral chambers, thus more 

 or less extensively obliterating the true walls. The corallites 

 are therefore really in close contact, and a true coenenchyma 

 is wanting. It may further be noted that there exists in the 

 present species a kind of undulating median partition (PI. 

 v., fig. 4 c), which seems to separate the corallites on opposite 

 sides of the frond, or to mark the line along which the four 

 longitudinal rows of corallites meet centrally. 



As regards other points of structural importance, tabulae are 

 very sparsely developed, and are not always detectable ; though 

 there can be no doubt of their general existence. Septa appear 

 to be wanting, so far as my observations go. Lastly, I have 

 not succeeded in demonstrating the existence of mural pores 

 to my own satisfaction ; but they are asserted to be present by 

 Dr Rominger, and I entertain no doubt as to the correctness of 

 his observations on this point. 



Formation and Locality. — Rare in the Hamilton formation 

 (Devonian) of Arkona, Ontario. 



