34 THE GENUS MONTICULIFORA. 



however, the comparatively trivial weight which can be at- 

 tached to the mere external shape, we find that the coralla 

 of the Monticuliporoids usually exhibit one or other of the 

 following conditions : — 



{a) The simply massive corallum, which is attached by one 

 point at its base, and may be more or less spherical or glob- 

 ose in form, or sometimes largely lobate. No epitheca is 

 apparently developed in such types, and occasionally {e.g., M. 

 irregiUaris, Ulrich) no basal point of attachment exists (the 

 corallum in some of these cases having grown round the stem 

 of a Crinoid). The simply massive corallum is seen in M. 

 tindtdaia, Nich., and occurs as a variation in some normally 

 laminar types {e.g., M. molesta, Nich.) 



{b) The discoid corallum, which has the form of a plano- 

 convex or concavo-convex disc, the upper surface of which is 

 occupied by the calices, while the lower surface is covered by 

 a striated and wrinkled epitheca, and may either be nearly flat, 

 or may be more or less deeply concave. In these cases there 

 is every reason to believe that the corallum was free. This 

 form of corallum is one very common among the Monticulipo- 

 roids, and is exhibited by various types which have no rela- 

 tionships in their internal structure. Thus, it is characteristic 

 Q)i M. petropolitana, Pand,, yJ/, Winteri, Wich., AI. petasi/ormis, 

 Nich., Af. .Selwyiiii, Nich., AI. Wkiteavesii, Nich., Prasopora 

 GraycE, Nich. and Eth. jun,, and some forms of Fistulipora, 

 in all of which the corallum, with some subordinate modifica- 

 tions, is of a proportionately considerable height as compared 

 with its width. The same type of skeleton occurs constantly 

 in Al. discoidea, James, AI. calyada, James, and AI. Newberryi, 

 Nich.; but in these cases the height of the corallum is greatly 

 reduced, so that it becomes more or less leaf-like. 



{c) The dendroid or ramose corallum, which consists ot 

 cylindrical or subcylindrical stems, which branch more or 

 less extensively, the base being attached to some foreign 

 object, and the entire free surface being covered by the calices. 

 More or less striking modifications of this type may occur by 



