I05 



CHAPTER VI. 



S/ib-ocjius Heterotrypa, Nich., 1879. 

 (Pal. Tab. Cor., p. 293). 



This section includes many of the most typical and most 

 familiar of the species of JMonticidipora, comprising- among 

 them the M. mamniulata, D'Orb., which, as the species first on 

 the list of Montindipora; given by D'Orbigny (Prodr. de Pal- 

 eont., p. 25), has the right to be considered as the type of 

 the whole orenus. In addition to M. viamimclata, D'Orb., we 

 must place here 31. raiuosa, E, and H., M. Andrezvsii, Nich., 

 M. Ulrichii, Nich., M. siibpulchella, Nich., M. G Ncalli, James, 

 M. Jamesi, Nich., J\L moniliformis, Nich., ]\I. tumida, Phill., 

 M. gracilis, James, and various other more or less certainly 

 established species. In all these forms the corallum is con- 

 spicuously dimorphic, and consists of two sets of corallites of 

 different sizes. The larger tubes are sub-polygonal or some- 

 times rounded in shape, and are more or less conspicuously 

 thickened towards their mouths, while they usually possess few 

 and remote tabulae, or may be in great part devoid of these 

 structures. They are usually to some extent contiguous ; but 

 they are always partially separated by the corallites of the 

 smaller series, which are also sub-polygonal, sub-angular, or 

 rounded, and more or less thickened towards their mouths. 

 In all the corallites the tabulae are complete, and the small 

 tubes are more closely tabulate than the large ones. Spiniform 

 corallites are often very well developed, but at other times are 



