13 
In the foregoing table I have endeavoured to portray, imperfectly I 
am afraid, the principal characters assigned to the two species by the more 
important authors. It exemplifies how diffcult it is to say, with our present 
imperfect knowledge of the two corals, what is II. catenularius, Linn., and 
II. escliaroides, Lamk., respectively. Upon this point depends, it seems to 
me, the validity of all other specific names from time to time proposed in 
Ilahjsites. It specific variation is to be accepted as of any value at all, more 
particularly as applied to stratigraphy, it appears impossible that such 
apparently different types, as for instance II. catenularius, Nicholson, PoSta, 
Lambe, &c., II. escliaroides , E.-B., II. clegans, P.-B., II. gracilis, Larnbe, the 
vars. quebecensis, Lambe, nilida, Lambe, simplex, Lambe, II cavernosa, P.-B., 
and many others, can be one or other of the restricted Edwardsian forms, as 
the case may be. llominger remarked 1 on the difficulty of arriving at specific 
separation through the “great variability of form” existing among his 
Michigan corals, but at the same time he appears to have been struck with 
the fact that “ various specific forms exist.” Prof. Nicholson and the Writer 
again, in 1880, wrote as follows : 2 — We hardly think that it is at present 
possible to define with certainty the different species of the genus Halysites. 
A very vast mass of material will have to be submitted to microscopic 
examination before it will be possible for the observer to assert positively 
whether the above-mentioned important structural differences arc constant 
and of specific value, or whether they are merely due to individual variation, 
or referable to other causes, such as the influence of sex, the temporary 
condition of the corallum as to the production of ova, or of the actual 
dimorphism or polymorphism of the species.” 
No one has more fully recognised the difficulties of specific determina- 
tion in this genus than Mr. Lambe, who says 3 : — “If an arrangement according 
to the outside form be attempted, or if the inner structure be relied on only 
as a basis for classification, it will be found almost impossible to arrive at 
satisfactory conclusions.” This expression of opinion is, however, somewhat 
discounted by the apparently contradictory statement that “ the variations in 
the general manner of growth of the corallum .... and the marked differences 
to be found in the inside structure appear to be sufficiently constant at 
different geological horizons to allow of varieties with certain characteristics 
1 Rominger, Report Geol. Survey Michigan — Lower Peninsula, 1S73- 76, III, Pt. 2, 1878, p. 78. 
2 Nicholson and Etheridge, Mon. Sil. Foss. Girvan, 18S0, Pt. 3, p. 276. 
» Lambe, Contrib. Canadian Pal., IV, Pt. 1, 1899, p. 65. 
