IOWA ACADEMY OF SCIENCES. 
259 
Measures of Iowa are known. The second part men- 
tioned is the “ Red Beds/’ which are developed to a thick- 
ness of 1,500 feet, clearly of Carboniferous age, and are 
followed by very similar ‘ 4 Red Beds ” which are of Triassic 
age. 
During the past two years I have collected and exam- 
ined a large variety of fossils from the Carboniferous rocks 
of New Mexico. My previous acquaintance with the forms 
of a like age in the Mississippi valley has enabled me to 
institute some critical comparisons between the faunas of 
the two regions. The close identity of the two has made 
a great impression upon me. Dorms from the New Mex- 
ico region which have been described under strange names 
have proved to be in reality very old friends. There are 
relatively a few species that are not common to the two 
regions. 
The conclusions reached in these studies have lately re- 
ceived remarkable corroboration in the results of Dirty’s 
studies of the Carboniferous fossils of Colorado.* In this 
memoir a large synonomy is given. Species after species 
are identified with Mississippi valley forms. In a very 
large majority of the forms treated of and discussed the 
species from Missouri are considered until it would seem 
that the Missouri reportsf could easily have been made the 
basis of the description of the Colorado species. 
The same is true of the New Mexican forms as disclosed 
by the recent work in this district. 
* U. S. Deol. Sur., Professional Papers No. 16, 1903. 
t Keyes: Missouri Geol. Sur., Vols. IV and V, 1895. 
