236 TABULATE CORALS. 



some of his conclusions, unless it were that some of the forms 

 which he refers to Thecia are really of a different nature. 



The affinities of the family of the Thecida will be best con- 

 sidered after I have given a short account of the structural 

 characters of the genus Thecia; and the group may be in the 

 meanwhile defined as including coralla formed of tubular 

 corallites of two distinct sizes, the larger disposed with con- 

 siderable regularity among the smaller ones. The large coral- 

 lites are tabulate, with indistinctly differentiated walls, provided 

 with obtusely triangular and irregular septa, and having their 

 visceral cavities more or less freely connected with one another 

 by lateral horizontal channels, which penetrate the interstitial 

 tubular tissue. The smaller interstitial tubes are doubtfully 

 tabulate, and their cavities are liable to be largely filled up by 

 a secondary deposit of sclerenchyma. 



Genus THECIA, Edwards and Haime, 1849. 

 Comptes Rend, t. xxix. p. 263. 



Gen. Char. Corallum rarely ramose, usually in the form of a 

 laminar expansion, covered below by a concentrically wrinkled 

 epitheca, and having the calices placed upon its upper surface. 

 Corallites in the main erect and perpendicular to the horizontal 

 axis of the corallum (sometimes slightly curved inferiorly), of 

 two sizes, large and small. The large corallites are placed at 

 regular intervals, and though their visceral chambers are clearly 

 circumscribed, they cannot be said to be bounded by distinctly 

 differentiated walls ; but they are, on the contrary, embedded 

 in a dense tissue composed of the smaller tubular corallites, 

 which may open on the surface by means of irregular, often 

 stelliform apertures, or may be to a large extent closed by a 

 secondary deposit of sclerenchyma. The smaller corallites are 

 primitively bounded by distinct polygonal walls, and it is not 

 certain if they are tabulate. On the other hand, the large 

 corallites are distinctly tabulate, are provided with irregular 



