SECTION [It [THE PUootlo 
GENERAL DISCUSSION OF THE FOSSILS 
After the appearance of the publication on Ozarkian and Canadian Brachio- 
poda, to which the present monograph is a sequel, brachiopod studies were con- 
siderably retarded by World War II. Nevertheless, some important ideas have 
been expressed. One of these has to do with the naming of the valves of brachio- 
pods. Hitherto the valves have been known as ventral and dorsal, but the work 
of Percival (1944) makes mandatory a return to the more cumbersome terms 
“pedicle” and “brachial,” + which are used throughout this monograph. 
CONCEPT OF FAMILY AND GENUS 
The same principles that guided Ulrich and Cooper in the preparation of the 
Ozarkian and Canadian Brachiopoda are used in the present monograph. The 
basis for uniting genera into families is again basically the pattern of the cardi- 
nalia combined with some constant features of the pedicle valve. Genera are 
then based on minor details of the interior deviating from the normal family 
pattern and the nature of the ornamentation and exterior form of the valves. 
Specific characters are found in minor details of the ornamentation and differ- 
ences in exterior form. 
SHELL STRUCTURE 
The writer has used shell structure as a guide in classification, but it is far 
too early to propose the nature of the shell as a basis of classification. Too much 
has to be learned about shell structure before it will have real value in defining 
major divisions. The arrangement of convenience used in the Shimer-Shrock 
“North American Index Fossils” (1944) has been misconstrued by some as a 
scheme of classification. It was not so proposed; the arrangement was designed 
to help the student separate brachiopods into easily recognized small groups in 
order to make identification easier. 
In the present work the shells are again divided for convenience into groups 
based on shell structure. In the endopunctate shells the genera and families are 
probably well grouped, but with the impunctate and pseudopunctate forms some 
difficulties are still to be mastered. For example, the orthoid genus Anomalorthis 
appears to have scattered pseudopunctae ; it is also well known through the work 
of Opik (1934) on the clitambonitids that some of these genera are pseudopunc- 
tate while others are without pseudopunctae. These difficulties cannot be re- 
solved in this monograph because much of the material does not permit detailed 
1In a recent note Percival discards his views of 1944 and indicates that the orientation of 
Terebratella inconspicua agrees with that of Tegulorhynchia and the pedicle valve is ventral 
in orientation. 
131 
