2 20 THE GENUS MONTICULIPORA. 



the surface than the preceding (fig. 46, c) show essentially the 

 same appearances as have been described above, but the walls 

 of the large coralHtes now appear to be reduced in thickness, 

 and there is a corresponding increase in the size of the smaller 

 interstitial corallites. 



Vertical sections (fig. 46, d) show, as their most important 

 feature, the very different tabulation of the large and small 

 corallites respectively. In the large corallites we find the 

 same type of incomplete tabulae as characterises M. Cincinnati- 

 ensis, James, M. Selivynii, Nich., and other species. That is to 

 say, the tabulse are bent downwards to form a series of over- 

 lapping lenticular vesicles on one side of the visceral chamber, 

 these vesicles (as shown in tangential sections) terminating on 

 the side turned to the axis of the tube, by a concave excavated 

 border. The remainder of the visceral chamber is either free 

 from tabulae, or is crossed by a few remote horizontal plates, 

 which pass from the line of vesicles on one side to the opposite 

 wall of the corallite on the other side. The small interstitial 

 tubes of the corallum are furnished, on the contrary, with very 

 numerous, complete, and horizontal tabulae. 



I have never seen a complete example of this species in its 

 adult state, though fragments three or four inches in length 

 and three or four lines in thickness are not uncommon. Young 

 and seemingly nearly complete examples (PI. V. fig. 4) may be 

 little over an inch in width or height, and only about a line in 

 thickness. These immature examples are generally smoother 

 superficially than large specimens, and differ in some other 

 trivial particulars ; but I have figured (PI. V. fig. /^a) a tangen- 

 tial section of one of them to show that in internal structure 

 they are essentially identical. 



It only remains to consider — and the point is one of unusual 

 difficulty — whether this form really is the M. froiidosa of D'Or- 

 bigny or not ; and on this head I regret to find myself at vari- 

 ance with some excellent observers, for whose opinions I enter- 

 tain the highest respect. Monticttlipora frondosa, D'Orbigny, 

 was originally described (Prodr. de Paleont., vol. i. p. 25) with 



