GENERA OF CH^TETID^E AND MONTICULIPORID&. 309 



their size is correspondingly variable ; but they are generally 

 of smaller diameter than the round tubes. The large corallites 

 are intersected by a few, remote, horizontal tabulse ; while the 

 tabulae of the angular interstitial corallites are much more 

 closely set, and become amalgamated in contiguous tubes, so 

 as to give rise to a vesicular tissue, the lenticular vesicles of 

 which have their convexities directed upwards. 



Obs. I have reproduced here the original figures of this 

 species (fig. 40), though they are in some respects incorrect. 

 The real structure of the 

 corallum is, however, shown 

 in PI. XV., figs. 3 - 3 d, from 

 which it will be seen that 

 its minute characters are in 

 the main similar to those of 

 Fistulipora minor, M'Coy. 

 It differs from this form, 

 however, in the larger size 

 of the round corallites, and 

 in the fact that any given 

 two of these are separated 

 by no more than one row 

 of the smaller tubes. Not 

 only are these latter mark- 

 edly angular in shape, but 



xv* 



Fig. 40. Fistulipora incrassata, Nich. a, A 

 fragment, of the natural size ; b, A portion of 

 the surface enlarged, showing the mouths of 

 the two sets of corallites ; c, A portion of the 

 surface less highly magnified, showing one of 

 the star-shaped "maculae;" d, Vertical sec- 

 tion enlarged. 



they, thus, necessarily abut 



on their opposite sides against the larger corallites. The large 

 tubes are not only oval, but they are wider at one end than the 

 other, and they usually exhibit the peculiar feature that there 

 exist two small inward inflections of the wall of the tube, which 

 are placed, one on each side, at a point situated about one-third 

 of the long diameter of the tube from its pointed end (PI. XV., 

 fig. 3 a}. Thin vertical sections (PI. XV., fig. 3 b) show that 

 the large corallites are intersected by a few complete horizontal 

 tabulse ; while the walls of the smaller tubes are imperfectly 

 developed, and their tabulae coalesce to constitute a series of 



