14 
being considered distinctive of the horizons in which they are found 1 and 
again : — “ It is found, however, that the Halysites of different geological 
horizons have distinctive characteristics which are apparently constant .” 2 
What is this but specific distinction ? 
On this horizon question, a previous writer, Prof. R. P. Whitfield, 
speakin g of the Halysites of the N iagara Formation of Wisconsin , remarked : 3 — 
“ It is also noticed that the specimens of the three varieties do not usually 
occur at the same locality, or if so, that some one of the varieties will greatly 
predominate, either at the locality or in a certain horizon, while the others are 
present only in limited numbers.” 
Either, therefore, Nicholson’s views of the di- or polymorphism of the 
corallum is correct, and equally so Lambe’s system of relegating all the 
Canadian forms but one to the position of varieties of H. catenularius is 
equally correct, the only differentiation being that of geological horizon ; or, 
on the other hand, there are more than the two principal specific types 
selected by Milne-Edwards and Haime. From the point of view of practical 
Palaeontology as an aid to stratigraphy, it appears to me the better course to 
pursue, pending the appearance of a complete Monograph on the whole 
supposed species constituting the genus, will be to regard all well-marked 
forms, such as many of Mr. Lambe’s are, as distinct species. This is the 
course I have pursued in regard to our Australian forms, for whatever may 
be the case with European and American species, I am able to differentiate 
the first both by external characters on a broad scale, aided by the internal 
structure. 
1 Lambe, Loc. cit., p. 65. 
J Lambe, Loc. cit., p. 67. 
• Whitfield in Chamberlin, Geol. Wisconsin — Survey, 1873-79, IV, Pt. 3, 1882, p. 271. 
