BEEDE AND ROGERS.] Coal Measures Faunal Studies. 859 
THE CHART. 
Inasmuch as the critical character of a fauna depends quite as much 
upon the nature of the faunal assemblage as the species present, the 
writers endeavored to produce a chart which would show this assemblage 
graphically. In order to accomplish this it was necessary to subordinate 
both alphabetic and zodlogic order to an order that possessed neither of 
these characters, with an added inconvenience of reference. For conve- 
nience of reference a separate list is published preceding the chart, with 
the classes or subclasses systematically arranged and the genera arranged 
alphabetically under them. 
The formations are arranged from below upwards, reading from left 
to right. The horizontal spaces represent the range of the species in 
these horizons. The fauna of any given formation is shown by the ver- 
tical column beneath its name. Several means of designating the occur- 
rence of a species in a horizon will be noted on the chart. In the first 
place, the upper part of the chart has a very different appearance from 
the lower part, on account of the blackened or half-blackened spaces. 
These spaces represent the relative abundance (percentage, roughly 
speaking) of the individuals of a species with those of any remaining 
species. To illustrate: We first took the species found in the lowest 
horizon (Cherokee shales) and found that Productus muricatus N. and P. 
dominated the whole faunule; that is, they were more abundant than the 
specimens of any other species. It was selected as the first of the list: 
and represented on the chart with a fully blackened space. Then it was 
found that there were four other species whose specimens played a very 
important part in the faunule and were more abundant than those of the 
remaining species. They were put in next in half-blackened spaces. 
The list from this horizon was then laid aside and that of the follow- 
ing horizon (Fort Scott limestone) was taken up and treated similarly. 
It was found that three of the species represented in the previous selee- 
tions were abundant in this horizon, and they were carried over in half- 
blackened spaces. It was found that Chetetes milleporaceous M.-E. and 
H. in places was so abundant as to form reefs and made up most of the 
bulk of the stone, and it was added in a fully blackened space, and then 
the remaining ten species which were found to be considerably more 
abundant than any of the remaining species were added in half-blackened 
spaces. It sometimes happens that two or more species are so much 
more abundant than any of the rest that they have to be represented by 
fully blackened spaces, as in the Florena shales. After the lists of all 
the horizons had been treated in this way, in which 111 species had been 
selected out, we returned-again to the lowermost horizon and added all 
the species which had not been represented in the 111 already used, and 
added them to the list. We then took up the list of the next horizon and 
added those species not already on the chart, and so on until the chart 
was complete. 
The lowermost horizon in which a species has been found is indicated 
by a cross with the left arm removed. In the Cherokee shales they are not 
marked in this way, as there is no way, at present, of determining how 
many of them may be represented in lower Coal Measures rocks in the 
Arkansas or other regions. The ordinary way of representing a species 
when present in moderate numbers or rare is by the full cross. When a 
species occurs for the last time this horizon is marked by a cross with the 
right arm removed. In case, however, it is suspected or known to occur 
in the Permian rocks above it is left with the full cross. Several such in- 
stances will be noted in the chart. In case it is confined to a single hori- 
