Stephan Pickering wrote-
Does anyone on the List know the present whereabouts of J.A. Clarke who, in 1999, briefly discussed Ichthyornis in an SVP abstract?
Can't say I do, but if you are interested in that paper, I recommend you acquire the following-
Clarke, 2001. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae (dissertation). New Haven: Yale University, Department of Geology and Geophysics. 457 pp.