SUB -GEN us HETEROTRYPA. 119 



Obs. — The name of Chcetctes sigillarioidcs was given by me 

 to this well-marked species in 1874; but my description was 

 not published (in vol. ii. of the ' Palaeontology of Ohio ') till the 

 middle of 1875, before which time Mr U. P. James had de- 

 scribed the same form under the name of C. O' Ncalli. This 

 latter name, as having the priority, must therefore be retained 

 for the species. 



In its external characters Mo7tticulipora C Ncalli is readily 

 recognised by its slender cylindrical, smooth branches, its 

 regularly oval, vertically arranged calices, and the presence of 

 numerous interstitial apertures between the upper and lower 

 ends of the larger calices (PI. III. fig. '^a). The openings of the 

 calices are often quite free ; but in other cases, often over con- 

 siderable areas, the large calices are closed by curious centrally 

 perforated opercula (PI. III. fig. 3^), which may be regarded 

 morphologically as representing the last formed tabulce. 



Tangential sections (PI. III. figs. 3(:, 3(^) show that the corallum 

 is composed of two distinct sets of corallites, large and small. 

 The larger corallites are oval, about i-iooth inch, or rather 

 less, in their long diameter, and, in this region, furnished with 

 thickened walls. Each tube (PI. III. fig. 3^/) is surrounded 

 by a ring-like wall of its own, and adjacent tubes are united to 

 one another by sclerenchyma, in which run the numerous small 

 corallites, these latter varying much in shape and size, but 

 being usually sub-angular. 



Transverse sections (PI. III. fig. 3^) show that in the cen- 

 tral region of the corallum all the tubes are thin-walled and 

 polygonal, only becoming thickened in the circumferential por- 

 tion. Lastly, vertical sections (PI. III. fig. 3/) show that the 

 corallites in the axial region are not only thin-walled, but also 

 remarkable in the shortness and slight curvature of their outer 



O 



thickened portions. These sections also show that tabulae are 

 nearly or quite absent in the centre of the stems, but developed 

 in fair numbers in the peripheral region, their direction, owing to 

 the slight curvature of the corallites, being often nearly parallel 

 to the outer surface. The small interstitial corallites are also 



