Using my "better / more persistent digital ferreting skills", I found this from a Toyota Media Preview.
From Scribd:
12Prius c Technical Presentation v3 2
2012 Toyota Prius c
Media Preview
La Jolla ● January 2012
Page 18, Slide 41:
3. Aerodynamic features
a. Aero stabilizing fins are installed on the side face of the rear combination lamp and at the base of the outer mirror
1) Initiates aero vortices that accelerate airflow along body side
2) Reduces weak boundary layer airflow near body and draws the main airflow closer to the body
3) Increases vehicle stability
4) Effective over 25 mph
b. Under body covers improve airflow
1) Smooth under body airflow
2) Vortex generators accelerate airflow
c. Lightweight aluminum wheels and wheel covers are designed with aerodynamic performance in mind
d. 0.28 Coefficient of drag