1. INTRODUCTION  
2. OBSERVATIONS AND DATA  
2.1. Sample Selection  
2.2. Keck Observations and Data Reduction  
2.3. Hubble Space Telescope Data  
3. KINEMATIC MEASUREMENTS AND STELLAR MASSES  
3.1. Line-of-sight Velocity  
3.2. GC Membership Criteria  
3.3. Systemic Velocity and Velocity Dispersion  
3.4. Stellar Mass Estimates  
4. RESULTS  
5. DISCUSSION  
5.1. Extreme UDGs in Virgo  
5.2. Less extreme UDGs in Virgo  
6. SUMMARY