CONCLUSION. 
The consecutive treatment of a group of organisms whose natural relations 
can be properly expressed only by diverging lines or ramifications from some 
common stock, fails to indicate satisfactorily the relations of each part of the 
group with every other part. These must be pointed out by themselves after 
the characters of the various subdivisions have been described. 
To avoid difficulties and unnecessary discussion, no recognition has thus far 
in this work, been accorded to family groups. The reasons for this will appear 
in the following. On the other hand it has seemed judicious, in order to 
make the generic discussions, as far as possible, homogeneous, to use as many 
terms of this value as are in any way justifiable. The future will undoubtedly 
demonstrate that some of these generic groups are still too broad. 
To regard the genus Lingula as taxonomically at the base of the brachiopoda, 
is a matter of custom. Against this position, nearly every feature of anatomy, 
development, and geological history is a protest. The muscular system of 
Lingula is extremely complicated, more so than that of any other of these 
inarticulate forms, and probably more than in any other generic group in the 
order of brachiopoda. In dealing with the fossil forms, the details of muscular 
arrangement are found to be frequently .much obscured; we can not always be 
sure of our data, and under such conditions, it becomes important to subordi¬ 
nate apparent variations in the arrangement of muscular scars, as an element 
in establishing generic relations, to some feature subject to less variation from 
mode of preservation. This feature of paramount importance, we believe will 
be found in the character of the pedicle-passage. 
Among the inarticulates, its variations in position and structure are extreme, 
and must have been accompanied by or have necessitated material changes in 
internal anatomy. On such a basis alone, Lingula, which has the posterior 
