John M Furneaux (ABT 1828-)
| +---James Trethewy (ABT 1517-ABT 1573)
| +---Richard Trethewy (BEF 1550-)
| +---Anthony Trethewy (-JUN 1625)
| | | +---William Hawkins
| | +---Joan Hawkins 
(ABT 1530-)
| +---Lewis Trethewy (AFT 1619-ABT 1693)
| | +---Elizabeth ? (-ABT 1644)
| +---John Trethewy
| | +---Elizabeth Arundell
| +---Robert Trethewy (ABT 1698-AUG 1771)
| | +---Elizabeth ? (-JAN 1708)
| +---Henry Trethewy (ABT 1734-APR 1784)
| | +---Grace Rogers (-SEP 1772)
| +---Henry Trethewy (ABT 1779-09 MAR 1869)
| | +---Charity Richards
+---? Trethewy
+---Ann Chambers (ABT 1776-04 JUN 1809)