+---Richard Trethewy (ABT 1665-JAN 1741)
+---William Trethewy (ABT 1694-)
| +---Ann Martyn 
(ABT 1666-JUN 1738)
+---James Trethewy (ABT 1719-)
| +---Jenefer Sweet (-SEP 1733)
+---James Trethewy (ABT 1746-)
| +---Grace Warne
+---George Trethewy (ABT 1783-05 DEC 1853)
| +---Elizabeth Carpenter
+---William Trethewy (ABT 1825-14 APR 1871)
| +---Elizabeth Roberts
+---Martin Trethewy (27 APR 1856-18 NOV 1936)
| | +---Ambrose Sprague
| +---Eliza Sprague (ABT 1824-)
| +---Martha Nicholas
+---Martin James Trethewy (27 JUL 1889-11 FEB 1970)
| +---Eliza Anne James (22 AUG 1862-10 MAY 1942)
+---Donald Garth Trethewy (26 APR 1919-28 NOV 1996)
| +---Maurie Vena Garth Scott (03 JUL 1893-05 JUL 1978)
+---David Martin Trethewy (09 JUL 1954-)
| +---Joyce Frances Phillips (11 MAR 1923-)
David Martin Trethewy (14 JUL 1978-)
+---Marcella Ann West (09 FEB 1954-)