GENERA OF CH^ETETID^E AND MONTICULIPORIDsE. 297 



proceeding to the extent that obtains in forms such as M. 

 (Heterotrypd) Jamesi, Nich., M. (Heterotrypa) tumida, Phill., 

 and allied types. The small corallites are very variable in 

 size and form, and are principally developed at the angles of 

 junction of the large tubes ; but they are commonly so numer- 

 ous as to form a complete zone round the large corallites, 

 though such a zone never consists of more than a single row. 

 Vertical sections (PI. XIII., fig. 2 a) show that the internal 

 structure of the large and small tubes is conspicuously different ; 

 both sets of corallites being traversed by complete horizontal 

 tabulae, which are greatly more numerous in the small tubes 

 than in the large ones. The " monticules " do not appear, as a 

 rule, to differ in structure from the general mass of the corallum, 

 but they seem sometimes to comprise a larger proportion of 

 small tubes than is usually the case in the intervening parts 

 of the skeleton. The internal structure of M. (Heterotrypa) 

 rugosa, E. and H., as I have elsewhere pointed out (Ann. Nat. 

 Hist, ser. 4, vol. xviii. p. 88), appears to be essentially the 

 same as that of M. ramosa, D'Orb. ; and the two are probably 

 but varietal forms of a single species. The only difference 

 between the two, in fact, is to be found in the marked trans- 

 verse elongation of the " monticules " of the former. 



Formation and Locality. Common in the Cincinnati group, 

 Cincinnati, Ohio. 



Sub-genus DEKAYIA, Edwards and Haime, 1851. 

 (Pol. Foss. des Terr. Pal., p. 277.) 



This section of the genus Monticulipora includes only one 

 or two types, which were separated by Edwards and Haime as 

 a distinct genus under the name of Dekayia, but which I regard 

 as forming a group of no more than sub-generic value. In the 

 general nature and structure of the corallum the species of De- 

 kayia entirely resemble the dendroid forms of Monticulipora^ 

 and the only feature that would strike the observer is that the 



