Palcontological Speculations. — Gratacap. yy 
is most evident, that literal species are more valuable, less 
stable than pelagic and abyssal forms, that the varieties of one 
period develop into the typical species of another, that this de- 
velopment attains a surprising rapidity in some instances, that 
faunas 'disa])pear. and again later, under presumably similar 
conditions, reappear. Dr. Sacco finds that variations of color 
are less important than those of form. He dwells, as many 
other observers, on the internal tendency and external circum- 
stances as constituting the two influences determining change. 
Amongst the latter are first, biological circumstances, as nutri- 
tion, enemies, parasites ; second, chemical, as nature of ocean 
floor, nearness of river mouths, material dissolved in the water ; 
third, physical, as light, conformation of the sea bottom, depth, 
temperature; fourth, mechanical, water movements. 
His canons of judgment in estimating change, are the ad- 
dition or diminution of features, and the gradual increase of 
one feature. He insists on the adequacy of the shells of mol- 
luscs to resolve the problems of this development. His es- 
pecial region of research, the tertiary basin of Piedmont, has 
furnished him with a most illustrative exemplification of these 
facts of variation, undisturbed by conditions of immigration, 
branchings, migration, etc. But he finds himself in carrying 
on the great work of Bellardi, involved in perplexities of ter- 
minology as to the limits and application of the terms sub- 
genera, variety, sub-species, sub-variety, forms, "mutations," 
etc. 
Studies of this nature amongst invertebrates have en- 
gaged American palaeontologists, and they have especially at- 
tracted the attention of Prof. Alpheus Hyatt. Dr. R. T. Jack- 
son, Prof. H. S. Williams, Dr. C. E. Beecher, Prof. J. M. 
Clarke and Dr. W. H. Dall. At present the examination in its 
entireness throughout the palaeozoics has not reached conclu- 
sive dimensions, and every additional contribution, if honestly 
conceived, cannot be regarded as imwelcome, unnecessary or 
inopportune. 
Prof. H. S. Williams in Bulletins 3 and 80 of the U. S. 
Geological Survey has discussed the changing facies of faunas, 
Devonian and Carboniferous, and has indicated ho.w variations 
have followed slightly changed conditions, and to what ex- 
tent, in the area considered, groups of associated forms com- 
