I04 THE GENUS MONTICULIPORA. 



few or wanting. The structure of the zuall, as in ahiiost all 

 the groups of Monticulipora, varies in different forms of the 

 group, according to the extent to which the originally duplex 

 character of the wall is preserved. In all, the tubes become 

 thickened and lamellated as the surface is approached ; but in 

 some (such as M. ttnnida, Phill., M. gracilis, James, &c.) they 

 become to all appearance so completely united with one 

 another in this part of their course, that thin tangential sec- 

 tions fail to show any traces of the original lines of demarca- 

 tion between adjoining tubes. In other cases (as in M. ramosa, 

 D'Orb., and its varieties), these lines of demarcation can be 

 to some extent recognised, though the apparent fusion has 

 largely obliterated them. Lastly, there are forms (such as M. 

 Trentonensis, Nich.) in which the primitive boundaries between 

 the tubes are quite well preserved, in spite of the thickening 

 of the walls. 



The section Heterotrypa includes many of the most typi- 

 cal species of Montiadipora proper, and it is also the section 

 most nearly allied to Fistiilipora, M'Coy. Its characters will 

 be more fully understood from the following descri^^tions of 

 illustrative species. 



Monticulipora (Heterotrypa) mammulata, D'Orb. 

 (PL VI. figs, i-ig.) 



Monticulipora iiiammulata, D'Orbigny, Prodr. de Paleont, vol. i. p. 25, 



1850. 

 Chcetetes juai/iinitlafi/s, Edwards and Haime, Pol. Foss. des Terr. Pal., p. 



267, PI. XIX. fig. I, 1851. 

 Monticulipora nianimulata, Edwards and Haime, Brit. Foss. Cor., p. 265, 



1854. 

 CJuntetes mammidatus, Nicholson, Quart. Journ. Geol. Soc, vol. xxx. p. 



508, PI. XXX. figs. 3-3(3!, 1874. Pal. Ohio, vol. ii. p. 207, 1875. 

 MoJiticnlipora i^Hcterotrypa) inajiiiuiilata, Nicholson, Pal. Tab. Cor., p. 294, 



PI. XIII. figs, i-i/', 1879. 



Spec. Char. — Corallum in the form of thin undulateci expan- 

 sions, from two to four lines in thickness, and often several 



