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, fiiils 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 genei'ic 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 



