I read the following text in the book Método de Latín I by Santiago Segura Munguía, published by the University of Deusto (emphasis mine on the words that cause me difficulty):
Multas fabulas a Graecis accepimus. Nobilis est fabula quae miram Iasonis Argonautarumque navigationem narrat. Iason, filius Thessaliae regis, cum rapere voluisset vellus aureum arietis, qui olim duos fratres per aera (por los aires) transportaverat, magnam expeditionem paravit (organizó). Rex Colchorum vellus aureum servabat, custoditumque erat ab immani dracone taurisque feris, qui flammas ore vomebant. Cum Iason immensam navem, quae Argo dicta est, construxisset, et in navem conscendisset cum Theseo, et Hercule multisque Graeciae principibus in Colchidem pervenit. Ibi a a Medea, regis filia, adiutus est. Cum Iason Colchidae regem post (después de) multos labores devicisset, vellus aureum rapuit et Medeam in patriam secum devexit. Cum Argonautae in Graeciam venissent, Olympicos ludos instituerunt, qui ab omnibus Graeciae populis semper celebrati sunt.
It seems to me that these three vellus should be vellerum: vellus is nominative singular, so it should be the subject or a predicative complement of the subject of the sentences, but I believe that this doesn't make sense. If vellerum was used instead of vellus, it would be the direct object of the sentences, something that makes complete sense. So, is this an error in the book? Or am I missing something?
The curious thing is that this book has been translated to Catalan and published by the University of Barcelona, but you can find the same text with these three vellus in the translation.
