188 The Auier/caji (jtulu(ji.sl. Marcli, 1897 
to ■' varieties" of OrUii.s testudlHaria which they could not de- 
line, nor that tlie common excuse " we thinl< the form in hand 
will prove to be a distinct species," wMiether written or reserved 
in the minds of authors, does not entirely negative the value 
of a new name. On the contrary, there seem to be many spe- 
cies with names to spare. 
The paleontological work in this series of papers comprises 
too little to justify much discussion on classification of Brach- 
iopoda. It may be said, however, that in the very promising 
materials examined, no case of the transition of one species 
or variety to another has been geologically traceable unless it 
be within K. minnesotensis Sar. from beds No. 1-4, or in. E. 
increhescens var. Inticosfata W. and S., but in most cases the 
biological relation remains doubtful except in so far as mor- 
])hoIogical similarity proves them to be clos?ly allied species. 
Paleontologists do not hesitate to describe new species from a 
single specimen, or from many specimens from a single local- 
ity and horizon, and presumably there can be error in the 
definition of a species. It is desirable, of course, to have large 
collections in order to learn the variations and mutations, if 
any, but what is most distinctly noticeable in the Galena and 
Maquoketa faunas, described by authors, is that species have 
been described not onl}- from insufficient materials, at times, 
but also from very abundant but poorly assorted collections. 
In a confused and badly collected set of fossils nothing is eas- 
ier than to slight the truth, both in respect to the definition of 
the individual species and in respect to faunas. 
In the groups of Orthis tesfu.duKiria auct. Plecfmnbunites 
sericea auct. and Rliiirichotielhi increbescens Hall (1847), 
one might have been led to expect abundant evidence 
of evolution from '-variety" to "variety." Careful in- 
vestigation, I think, proves that the evidence is from 
a biological source mainly, and that the addition of 
geological evidence necessitates new conclusions. The species 
("varieties") succeed each other in a manner such as to prove 
their relation not to be that of "local varieties." They enter, 
as a rule, independently, quickly, and in the same order over 
the entire area, and thus they may be used to distinguish the 
ditTerent contemporaneous strata at distant localities. In the 
Bull' limestone bed (1) the Bhi/nchotiel/a cL ortoitalis forms 
