All this talk about distal femur bits and potentially crumbled into oblivion neural arches in Amphicoelias is slightly deceptive. The only species missing all of its evidence in this discussion is A. fragilimus. There is another, smaller, species described in the genus Amphicoelias: Amphicoelias altus. Amphicoelias altus is actually the type species of the genus and is composed of a number of bones including the scapula, ulna, a tooth, coracoid, pubis, femur, and two vertebra; the type fossil consists of the last three structures mentioned with the first four being found later. Mook, mentioned yesterday, noted that Amphicoelias, based on A. altus, is very similar to Diplodocus; however, the proportions of limb length in A. altus are significantly, relatively speaking, different from those of Diplodocus making it a taller animal though they are of similar length. Due to the similarities some have proposed that Amphicoelias is a senior synonym of Diplodocus, but the overwhelming majority assert that the differences are enough to warrant the occupations of both names as valid and separate genera. Another species has been proposed recently, A. brontodiplodocus, but this species has been refuted by many and the lead author of the unpublished paper, Henry Galiano, has noted that the proposition of the idea of one genus with many growth stages of sauropod represented and currently named as separate genera from the Morrison Formation, the essential theme of the work, is not ready to be published and is not, thereby, ready to be criticized. We shall see if they develop the idea further, but if you are interested in it you can read what has been circulated so far and you can read two analyses by Mike Taylor and Matt Wedel, respectively. As for my opinion of the matter, I reserve the right to review everything and not post it online, as I do not consider myself enough of a sauropod expert to weigh in at this time.