GENERA OF CH^ETETID^E AND MONTICULIPORIDsE. 317 



Corallites directed upwards nearly at right angles to the entire 

 basal plate, and opening upon the upper aspect of the colony. 

 Surface with scattered and very slightly raised " monticules " 

 composed of corallites slightly above the average in size. 

 Corallites of two kinds, large and small, the tubes of both 

 series intermingled throughout the entire corallum. Large 

 tubes, mostly from a sixth to a fifth of a line in diameter, 

 more or less thin-walled, angular, often hexagonal, in shape, 

 and sometimes arranged in small groups or rosettes of four 

 or five tubes each. Small corallites very numerous and very 

 variable in size and form, but always thin-walled and angular, 

 and wedged into all the interspaces left between the large 

 tubes. In internal structure the large tubes may be simply 

 crossed by remote, delicate, complete tabulae ; but many of 

 them are divided by a vertical flexuous partition into two 

 compartments, the tabulae on the one side of this partition 

 being strongly curved, with their convexities directed up- 

 wards, while on the other side they are simply horizontal. 

 In the small tubes the tabulae are always very numerous, 

 close-set, and horizontal. 



(9fo. In general form, the corallum of the present species 

 (fig. 42, and PI. XIII., figs. 4, 4 a) is generally quite like that 



Fig. 42. Monticulipora (Diplotrypa) Whiteavesii. A, Side view of the corallum, of the natural 

 size ; B, Transverse section of the corallum near its base, showing the thin-walled hex- 

 agonal corallites, enlarged. (This section cuts across the axial corallites close above their 

 origin, showing none of the small tubes, the appearances presented being thus quite unlike 

 those exhibited by a tangential section taken just below the surface, as in PI. XIII.. fig. 

 4 b) ; c, Part of a vertical section, greatly enlarged. 



of the typical M. petropolitana, Pand., with which it has gener- 

 ally been confounded by myself and others. When young it is 

 a concavo-convex disc ; but it usually becomes elevated and 



