The Niobrara Chalk, — Calvin. 157 
excrescences, and again the later chambers may be simply 
heaped together in inextricable disorder. Everything suggests 
abnormal, if not positively diseased, conditions. The depau- 
perating effects of unfavorable environment seem to have 
acted in three ways : first, to retard growth and thus produce 
the pygnnean type; second, to cause deformity by unsymmet- 
rical growth even when the biserial arrrangement is main- 
tained; third, to interfere with the biserial arrangement of 
the later formed chambers among the more vigorous individ- 
uals, and to produce all possible types of departure from 
normal regularity. 
In all the thousands of specimens examined I have seen 
nothing corresponding to Bailey's figure of Textularia ameri- 
cana, nor have I been able to recognize as many species as 
Ehrenberg described from the region along the Missouri. 
There are endless variations, many of which would doubtless 
have been formerly regarded as of specific value; but, after 
all, I can see no reason for regarding all the textularians of 
the region, with their countless variations as to size and pro- 
portions, including departures from symmetry and biseriality, 
as other than varieties of a single species which for the pres- 
ent we may call Textularia globulosa Ehrenberg. 
While Textularia seems to have flourished best in the 
deeper and purer waters remote from shore, the reverse is true 
of another group of forms that have usually been identified 
with Ehrenberg's Rotalia globulosa or Rotalia aspera. Ac- 
cording to Brad} T , these may all be referred to the genus 
Globigerina and represent a single species, the Globigerina 
cretacea of d'Orbigny. The forms in question present a wide 
range of variation among themselves, but the average or ideal 
consist of one or two spirally arranged whorls of rapidly in- 
creasing globular chambers the walls of which are thin and 
perforated by relatively large foramina. Among the depart- 
ures from the average type there are some with few. large 
chambers, agreeing well with G. bulloides; while in slides from 
Saint Helena there are occasional individuals in which the 
last chambers are curiously elongated so ,-is to imparl to the 
entire shell an aspect identical with Brady's species, Globig- 
erina digitata. The earlier formed chambers are in all re- 
spects like those of the typical Globigerina cretacea, &nd it 
