IOIO Zoic Maxima, or Periods of [December, 
illustration, for, as pointed out by Professor Whitfield; the dimin- 
utive fossils of some molluscous species found at Spergen hill 
became, at Paynter’s hill, a little over a mile west of the former 
locality, much larger, while the Bellerophon and Euomphalus of 
the Ellettsville, Ind., beds, greatly exceed in size the same spe- 
cies from Spergen hill, and in a less striking way collectors have 
become familiar with certain localities where certain fossils as- 
sume an unusual or handsome size contrasting with their depau- 
perate appearance elsewhere. 
A great deal of instructive and careful study has been expended 
in recent years, since the advance of research has made natural- 
ists better acquainted with the oscillatory character of faunal 
populations, upon the perplexing question of the contemporaneity 
and succession of fossil faunas, and Barrande, Etheridge, Hall, 
Hull and Gosselet abroad, and Williams, Walcott, Call, Clarke 
and Matthews at home, have pointed out some of the details of 
their results in this investigation, and have already familiarized 
the scientific world with the important conception that varietal 
faunas or modification of a central or controlling animal facies, or 
even sharply contrasted zodlogical aggregations of species may 
belong to the same epoch and be laid down in the neighborhood 
of each other on the same oceanic or lake flooring. 
Our intention here was not to discuss the variations of specific 
forms in the fossil-bearing rocks as throwing light upon the syn- 
chronous existence of different faunas, their succession, retreat, 
reappearance and fusion. It is undoubted that these assumptions 
explain and are indeed the chief explanations to be offered for 
the varying character of near-lying fossil groups; but we wish to 
urge upon the consideration of palzontologists the necessity of 
allowing—as far as regards the instances of fossil distribution cited 
above, viz., the greater or less prevalence at near horizons or beds 
or along the horizontal extension of the same bed of the same 
fauna or species—for those irregularities of production of life, 
which cause in our present seas different years to become dis- 
af : tinguished for a phenomenal abundance of certain forms, as 
_ Others to claim a distinction for the abnormal decrease or disap- 
pearance of the same forms over the same geographical area. 
= Thus a given spot on a coast line, always yielding a particular 
__ Species, may in one season become the abode of numbers of these 
T 
e i | Amer, Mus. Nat. Hist., Vol. 1, No. 3. 
