HCR diary 26.11.1826 at Lamb's - Arnold nephew of Ayrton and Moxon
24.12.1836 "to the Aders wher I found young Arnold and his wife - I had seen him at Ayrton's and Lamb's but was not aware how impertinent and rude a young man he is. I know not when I have seen so offensive a man. He is a nephew of the late Mrs Ayrton".
Thomas James Arnold (DNB 1803-1877) son of Samuel James Arnold (DNB 1774-1852) who was son of Samuel Arnold (DNB 1740-1802). William Ayrton (DNB 1777-1858) married Marianne, daughter of Samuel Arnold. Marianne Ayrton was buried 1.2.1836 from James St at St Margaret's Westminster. If Crabb Robinson meant that Arnold was also a nephew of Edward Moxon (DNB 1801-1858) a friend of Charles Lamb's who later married Lamb's adopted daughter, I haven't found any such relationship