THE MONTICULIPOROIDS. 



347 



than the average (fig. 224, mo). The walls of the tubes are imper- 

 forate ; tabulae are always present • and true " septa " are probably 

 always wanting, though " pseudosepta," in the form of radial plates 

 or spines, are in rare cases developed. 



The form of the skeleton in the Monticuliporoids is extremely variable, 

 though it is in general tolerably constant for each species. In many 

 forms the skeleton is dendroid or ramose (fig. 224, B), consisting of 

 cylindrical or subcylindrical stems, which have a fixed base and branch 

 more or less freely above, the entire surface being covered with the 

 openings of the tubes. In others, the skeleton is so far modified from 

 the preceding that it assumes the form of an erect, laminar or frondescent 



Fig. 224. — a, Fragment of the frondescent corallum of Monticulipora mammidata, D'Orb. 

 ( — Peronopora molesta, Nich.) showing " monticules " (mo) ; b, Fragment of the dendroid corallum 

 of Cailopora? (Heterotrypa) rugosa, E. and H. ; C, Discoid corallum of Amplexopora discoidea, 

 James; d, Hemispherical corallum of Cailopora nummrformis, Dyb., viewed sideways ; e, The 

 same vertically fractured, showing the divergence of the tubes and the peripheral "mature" 

 region (;;z). All the figures are of the natural size, except e, which is reduced. (Original.) 



colony, composed of two strata of tubes the mouths of which open on the 

 two sides of the expansion (fig. 224, a). In numerous other types (fig. 

 224, d) the colony is hemispherical, the usually flattened or concave base 

 being covered with a concentrically wrinkled epitheca, while the mouths 

 of the tubes cover the entire upper surface. In still other forms, the 

 tubes are very short, and the colony has the form of a thin, flat or concave 

 disc, with a striated basal plate (fig. 224, c). In other cases, the skeleton 

 assumes a lobate or massive form ; and in others it is encrusting, and is 

 attached parasitically to foreign bodies. 



A very important distinction between different types of the Mon- 

 ticuliporoids is based upon the homomorphic or heteromorphic con- 

 dition of the colony. In some forms (viz., in Monotrypd) the tubes 

 are essentially similar throughout the colony in size and internal 

 structure, any difference which may be observed between different 



