Permian Formation of Texas. 
Gervillia longa Geinit 
Aviculopecten occiden 
SUMMARY. 
( Cephalopoda 1 1 species. 
, Gastropoda 
Articulata, \ Crustacea i " 
Radiata.... Polypi i 
Total, 32 
By reference to the foregoing^ list of species, and especially to the 
summary at the foot of the list, it will be seen that the invertebrate 
collections which have hitherto been made from the Permian form- 
ation of Texas, do not represent a fauna in its usual proportions, 
as regards the classes and families to which the species respectively 
belong. This is especially true when we compare these collections 
with Permian faunas already known in other regions. For exam- 
ple, it will be seen that the Cephalopoda are in unusually large pro- 
portion, that the Brachiopoda and Polyzoa are absent, and that the 
Polypi are represented by only a single species. In short, it is plain 
that the invertebrate fauna which existed during the period in 
which the Texas Permian was depDsited, and in the same, or in 
contiguous waters, is imperfectly and disproportionately represent- 
ed by these collections. 
Some of the causes of the imperfection and disproportion refer- 
red to, are too plainly apparent to need extended comment, and 
others are suggested by the lithological and stratigraphical charac- 
ter of the formation in which the remains are found. Besides the 
inevitable causes of imperfect representation of extinct faunas by 
their remains, a conspicuous reason for the imperfection of these 
collections is that the formation has yet been carefully examined in 
only a small part of the large region which it is known to occupy, 
and an exhaustive search for invertebrate fossils has yet been made at 
only a few of the localities which have been visited by competent 
collectors. 
Again, there are few strata entering into the composition of the 
Texas Permian where it has been examined, the character of 
which indicates that they successively formed the bottom of waters 
where at least a large proportion of then existing invertebrates 
