lord byron says "alas, poor prim"

Judith Blunt-Lytton, Lady Wentworth, was a great-grandchild of Lord Byron and a noted authority on Arabian horses. She did write one book on toy dog breeds, in which she offhandedly notes this jewel of a family anecdote:

A liking for dogs runs in my family. Lord Byron, my great grandfather, wrote verses on his own dog which are too well known to quote, but the epitaph he wrote on a pet dog belonging to Lady Byron is not so well known:
 Alas, poor Prim,
I'm sorry for him.
I'd rather by half
It had been Sir Ralph.
Sir Ralph Milbanke being his father-in-law, the verse has the usual caustic Byronic vigour.

I couldn't find any images of Prim, but I did turn up this Guardian pictorial article on Byron's dogs, if you're interested.

 -  Wentworth, Lady, 1873-. Toy Dogs And Their Ancestors: Including the History And Management of Toy Spaniels, Pekingese, Japanese And Pomeranians. London: Duckworth, 1911. p. 7.