INTRODUCTION

2. SAMPLE SELECTION AND STELLAR-MASS ESTIMATION

2.1. The NuSTAR Serendipitous Survey  
2.2. Multi Wavelength Counterpart Identification  
2.3. The NuSTAR Low-Mass Galaxy Sample  

3. DATA ANALYSIS

3.1. SED Fitting and Stellar-Mass Estimation  
3.2. Basic NuSTAR Properties  

4.1. The Optical and X-Ray AGN Diagnostics  
4.2. Optically-Dull X-Ray AGNs  
4.3. Identifying Heavily Obscured AGNs in Low-Mass Galaxies with NuSTAR  

5. COMPARISON WITH PREVIOUS STUDIES

5.1. Mid-IR Colors  
5.2. $M_{\bullet}\!-\!M_{\star}$ and Eddington Ratios  
5.3. X-Ray Properties  

6. DISCUSSION AND CONCLUSIONS