130 Cincinnati Society of Natural History. 



upon in separating the species. In Alveolites siiborbicularis the 

 pecuHar habit of forming irregularly gibbous masses, composed of 

 successive concentric strata enveloping some foreign body "is only 

 found in specimens which have a special internal structure; under 

 these circumstances it becomes a character of specific value."'* 

 Again the same is the case with two species of Colum7iaria, C. cali- 

 citia and 6. alveolata, and the external feature alone is useful in 

 making the separation. f Take again the following: "It would 

 appear, .... that so far as at present known, there is noth- 

 ing in the internal structure of CladochoDia, McCoy (= Fyrgia, E. 

 & H.,) which would separate it from Aidopora, Goldf. , and the 

 generic distinctness of the two can only rest upon the feature that 

 the corallum of the former is erect, whereas in the latter it is creep- 

 ing and parasitic.";}; In speaking of the differences between 

 Dekayia and Motiticulipora the same authority states that the general 

 nature of the corallum is the same in each, "and the only feature 

 that would strike the observer is that the surface of the former is 

 studded with little quadrangular spines or columns, interspersed in 

 great numbers among the ordinary tubes of the corallites."§ 

 Between M. rainosa and its variety rtigosa there are striking external 

 differences, yet "the more minute external and internal characters 

 of M. rugosa, are precisely similar to those of J/. ramosa."\\ 

 Under the name of M. undulata, Dr. Nicholson places two forms 

 having the same internal structure, but being very different in form. 

 One forms "large, lobed or laterally indented masses"; the other is 

 smaller, hemispherical or spheroidal, "of from half an inch to more 

 than an inch in diameter."^ So, too, with Mr. Ulrich's species. 

 In the description of M. consimilis, which we shall place as a 

 synonymn under M. cincinnaticnsis, he says the internal structure is 

 almost exactly like his M. Imis, which we shall place as a variety 

 of M. hospitalis, Nich.° These are by no means the only examples 

 which could be quoted, but they will show that the internal struc- 

 ture is not a more infallible guide than the external one, besides 

 laboring under the additional disadvantage of requiring a much 

 greater amount of work, which may, in the end, prove valueless. 

 For the purposes of discrimination of species, therefore, mainly 

 the object of this paper, the authors shall lay stress upon external 

 features, believing it better to take obvious features rather than 



*lbid. p. 127. f Tabulate Corals, p. igS. Jlbid, 223. 



^Geniis Monticu., 98, 99. 



IIGenus Montic. 114. 



IT Ibid- 17--73- 



oj. C. S. N. H. V. 238. 



