On the Monticidiporoids of the Cincinnati Group. 1 29 



ing, close the mouths of cells, each operculum eventually forming 

 the base of a new cell, the central foramin being closed. 



Fourth. — Certain smaller cells or tubes are known as inter- 

 stitial. These have distinct walls, and at the same time have more 

 numerous diaphragms than the other tubes. The diaphragms are 

 always complete and approximately straight. While in the sub- 

 genus FistuUpora the corallites are separated from each other by 

 interstitial tubes, in the true Afonticiilipora, the larger tubes are, to 

 some extent in contact, and the tabulae of the smaller tubes do not 

 become vesicular. "At the same time," says Dr. Nicholson, ''it 

 must be admitted that there are some species of Monticulipora 

 which make a close approach to FistuUpora, and that it is not 

 always an easy matter to separate the two genera."* 



Fifth. — Spiniform corallites or tubuli, are blunt, spine like 

 structures, placed either at the angles of junction of the cells, on 

 the line separating adjoining cells, or included in the walls of the 

 cells. These are found in a large number of species of Monticuli- 

 pora, but can not be regarded as of classificatory value. f This is 

 also the case with opercula, as "it does not appear that the oper- 

 cula are developed in any uniform manner, some parts of the sur- 

 face showing these structures, while in other parts the calices are 

 open.";}: 



Now as the external features have been condemned by Messrs. 

 Nicholson and Ulrich, the two special workers in the field so often 

 quoted, and they lay such stress upon the internal characters, let 

 us see if these can be depended on to any greater extent. We 

 think it can be shown that these features of the Monticuliporoids 

 are as unsatisfactory as the external ones are to them. To our minds 

 they are much more unsatisfactory, because they entail an immense 

 amount of work which in the end seems to amount to very little. The 

 extracts following will give an idea of the little dependence to be 

 placed upon species based solely, as some have been, on internal 

 structure. In speaking of the separation of two genera, Dr. 

 Nicholson says; "There is, indeed, no feature in the way of in- 

 ternal construction which could be brought forward as separating 

 Striatopora from Pachypora; and in distinguishing these two types 

 we have to fall back upon a well marked external character. "§ In 

 the following case peculiar external form is connected with peculiar 

 internal structure, and the former circumstance is generally relied 



*Genus Monticu., p. 97. fibid, p. 49. J;Genus Monticu., p. 55. 

 ^Tabulate Corals, p. gy. 



