PREFACE. 23 
correct account of the species belonging to his 
own country. 
It is proper to state here, that when the work 
was nearly ready for publication the annexation 
of the republic of Texas to the United States 
enlarged the area of the author's investigations, 
by the addition of a region of many thousand 
square miles in extent to the vast territory already 
included in the field of his inquiry. He endeav- 
ored to meet the exigency by employing a com- 
petent naturalist to explore the accessible parts 
of that State during the early part of 1846 ; but 
it cannot be expected that the results of that ex- 
ploration can exhibit more than an incomplete 
view of the species living there. A wide field 
of investigation is left for the future naturalist, 
both in Texas and in the whole extensive and 
but partially-explored region west of the Missis- 
sippi river. 
The author takes pleasure in making this 
public acknowledgment of his obligations to those 
gentlemen who luwe kindly furnished him with 
materials used in the preparation of the work. 
To B, E. Griffith, M. D., late of the University 
of Virginia, a cotemporary of, and fellow-laborer 
