118 Permian Formation of Texas. 
iferous species. The F iyc hi ies dind Popanoceras maybe properly re- 
garded as of mesozoic type, such as might be expected to occur in 
Triassic strata. The Medlicottia is the first species of the genus to 
be discovered on this continent, and has been usually regarded as 
indicating the later Carboniferous, or Permian age, of the strata 
containing the genus. 
EXPLANATION OF PLATE L 
COPEI. 
Lateral view. 
Outline showing transverse section of voluti 
" 6. Lateral view of a larger example. 
7. View of a septum of a larger example. 
" 8. Suture line of the same. 
POP.\NOCERAS WALCOTTI. 
" 9. Lateral view of a small example. 
" 10. Peripheral view of the same. 
All the figures are a little less than natural size. 
It will be seen from the foregoing descriptions and notes, that 
of the 32 species of invertebrates which are represented in the col- 
lections from the Texas Permian, only four of them are recog- 
nized as new, all of which are cephalopods, and all belong to the 
Ammonoidea. The others have either been previously described 
and published, or their specific identity with published forms is in 
doubt because of their imperfection, either of the specimens in 
hand, or of the manner of publication of the species which they 
probably represent. Fifteen of these Texan species are satisfacto- 
rily recognized as having been previously published, a part of which 
have been by some authors referred to the Permian, but the Coal- 
measure age of the remainder has never been questioned. Some 
authors also assert that not only all of the fifteen species just men- 
tioned, but all North American invertebrate species which have ever 
been referred to the Permian, are really members of the fauna 
which characterizes the Coal-measure period. Indeed, so generally 
has this view prevailed during the last twenty years, that if the four 
new cephalopods before mentioned were not present in the Texan 
