14-i 7/i' AuurlcdU Geologist. September, ISOl 
the river, just below the mill at Littleton, the Acervularia prof unda beds 
rise only a few feet above the level of the water. Farther down the 
stream they are better exposed. 
6. Arerrnhirid diiriihiiiii hedx. These beds lie upon the A. profunda 
beds. The transition from one species of Acervularia to the other is 
very abrupt. There are layers crowded with -1. jirnfnnihi Hall, in the 
lower part of the bank of the river, and two or three feet higher tlie 
rock is simply a compacted mass of ,1. da rid. son i Ed. and H. The two 
species never occupy the same layer, and furthermore the two are here 
as distinct as any tw^o species of the same genus could be by any reason- 
able possibility. In mode of growth, size and depth and essential char- 
acteristics of the calj'ces of the individual corallites, development of 
the septa, and indeed in all particulars that make up specific distinctions, 
.1. profniiilii Ilall, and .1. duridsn/ii Ed. and H., are at least at Littleton, 
Iowa, specifically far apart. This much is said for the reason that so 
eminent an authority as Kominger regards .1. profundu as merel}' a 
variety of the species A. daridmni. 
In layers associated with the A. davidsoni beds, though not in the 
same layers with the corals, are found specimens of Spin/era parryano 
Hall. As I have elsewhere observed* the beds that furnish S. porri/ioiit 
always lie above those in which ,s'. penndtn occurs. This relation is well 
illustrated in the rocks of Buchanan count}'. Along with A. davidsoni 
occur a number of species of Fiinixttis and one species of ('h<ii,i,phylhuii. 
The same Fiirosiiis and Choaophnlliini are associated with ^i. duchhoni 
and S. parryniid at Iowa City, in Johnson county, Iowa. The A. david- 
soni beds at Littleton furnish some beautiful examples of Pentamerelhi 
dfihiii Hall, a species that occurs at the same horizon near Iowa City. 
Neither Atri/pn asperK nor any form of spiniferous Atrypa, is known 
from beds, number fi, either in Buchanan county or elsewhere in Iowa. 
These beds with their ^1. d<iridsi)/i/\ FiicoKitix, Sjiirifi-ni pdrrifunn, and 
other distinguishing characteristics are well developed along Lime 
creek, near Brandon, in the southeast corner of Buchanan county. 
7. Ydloir x/iiih beds. At a considerable distance above the A. david- 
soni beds, with probably some characteristic beds between, occurs a bed 
of yellow colored shales. These shales are exposed well up in the river 
bank below the mill at Littleton. The fauna is peculiar in this respect, 
that nearly all the forms are strangely modified. Atrypn vetioihirix Linn, 
vs very coarsely- ribbed, with the ventral valve fiat or concave and the 
dorsal valve excessively gibbous, contrasting strongly with the form from 
tlie Spirifera pennata beds. SI rojilunlnnfii dcmixxd Con., is large, the 
hinge line often exceeding two inches, and the width of the shell fre- 
([uontly more than twice the length, ('yrtiim liiiniilfunciixix Hall, is a 
diminutive affair having, on an average, less than one-fourth the normal 
dimensions. A Spirifer which may be a modified S. p(irryinifi,h\ii de- 
serving to rank as a distinct species, has the hinge area much narrower 
W'o/i'n on //if Si/iioiii/iii;/, ClKiractei'ii and D'ustrilintion of Spiriffra parryana Hall. 
Jinih'lin from the Lnli'ordloriex of XrdKrnI Hittonj of the State Unirerxitij of Iowa. 
Vol. I. Xo. I, !>. 25 et HiMi. 
