Wheelock introduces 'Laocoon, -ontis (m)' as the character in a story. However in the text, the form 'Laocoonta' appears. The -is genitive ending means that it is 3rd declension no? With endings in -em, -is, -i, -e, -es, -um and -ibus. So how can a masculine 3rd decl noun end in '-a'?