114 Cincinnati Society of Natural Fiistory. 
valves have a more tumid aspect, and the two or three lobes appear 
more like rounded prominences than ridges. 
The ‘‘tri-sulcate’’? species of Beyrichia, the majority of which 
I believe ought to go with: Boliia, are also related, but not so closely 
as may appear at first sight. In those species it seems to me the 
sub-centrally situated horse-shoe ridge characterizing the true 
Bolla is simply no longer fully developed, the definition of the 
sulci having gradually disappeared in the ventral half of the valves. 
In all species of olla, including the aberrant forms just alluded 
to, the central sulcus is approximately vertical, while the two lat- 
eral ones curve away from the center. In TZeftradella, however, 
such a bilateral arrangement is not evident, since it is generaliy 
the case that a// the sulci curve more or less anteriorly. 
Species of this genus have a greater vertical range than 1s usual. 
Thus, specimens apparently identical with 7Z. chambersi occur 
already in the Birdseye, at which horizon I collected them in Min- 
nesota. I have not yet seen the typical form in the Trenton 
proper, but a variety in which the process is less spine-like and 
its fringed edge semi-circular, occurs in the upper beds of the 
Trenton and in the lower or Utica horizon of the Cincinnati 
Group 
This variety probably foreshadows the Z° oculifera, a form that is 
so far as known restricted to the uppermost one hundred feet of 
the strata exposed in the Cincinnati hills. Another variety of 
T. chambersi, differing from the typical Cincinnati specimens in 
having the two anterior ridges or lobes fuller, and the third or 
postero median one much larger than usual, occurs in the upper 
beds of the group at numerous localities. This form was illus- 
trated a Hall and Whitfield, from Waynesville, Ohio (Pal. Ohio, 
Vole Pl IWe test Gite marta): 
TZ. ne and 7° szmplex also occur in the BEEee lime- 
stone of Kentucky and Minnesota, but appear to be absent in the 
beds intervening between that horizon and the upper two or three 
hundred feet of the Cincinnati Group. 
