i8o THE GENUS MONTICULIPORA. 



and becoming slightly thickened towards their mouths, but 

 always retaining their original boundary-lines. They are all 

 of one kind, sub-equal, from i-yoth to i-8oth inch in diameter, 

 being rhomboidal in shape in the centre of the branches, 

 but often becoming pentagonal as they approach the surface. 

 Calices often polygonal, but usually in parts obliquely rhombic, 

 and arranged in regular diagonal rows, the direction of which 

 changes within short distances, thus communicating to the 

 surface a characteristic aspect. No monticules or maculae are 

 present, and the lips of the calices are thin. Tabulae appear 

 to be wanting, or to be very sparingly developed, in the axial 

 reeion of the corallum ; but there exists a considerable number 

 of complete, straight, or slightly curved tabulae in the outer 

 thickened portion of the corallites, the tabulation of all the 

 tubes being alike. 



Obs. — Superficially, this species is readily distinguished from 

 the other dendroid species of Alontiailipom by the commonly 

 rhombic or diamond-shaped form of many of the calices, these 

 openings being then arranged in curved diagonal lines, which 

 cross each other obliquely. Even when the calices are simply 

 polygonal, as is sometimes the case, over large parts or over 

 the whole of a given specimen, this characteristic appearance 

 may still usually be recognised by an examination of the 

 weathered ends of the stems where the invariably rhomboidal 

 tubes of the axial rcQfion are brouQ-ht into view. The re- 

 maining superficial characters that are of the most importance 

 are the want of marked thickening in the edges of the calices, 

 and the total absence of small interstitial corallites, as well as 

 of monticules or of groups of either large or small tubes. 



As regards its internal structure, M. qnadj'aia, Rominger, 

 exhibits characters of such marked peculiarity, that there is no 

 other species of the genus, so far as I know, with which it 

 requires to be compared. In the axis of the branches, the 

 corallites are always provided with very thin and delicate walls, 

 and have no tabulae, or hardly any. In this region, also, as 

 shown by the central part of a transverse section (fig. 36, d). 



