312 Abstracts of poster demonstrations functional demands of the post-larval stage in a species' life history (possibly quite different to the adult period) are quite important. Differences in the relative rate of disc plate and arm development between some direct and indirect species and shallow and deep sea forms are tentatively suggested. Preliminary observations on the near-bottom ichthyofauna of the Rockall Trough: a contemporaneous investigation using commercial- sized mid water and demersal trawls to 100 m depth N. R. Merrett and J. Badcock Institute of Oceanographic Sciences, Brook Road, Wormley, Godalming, Surrey GU8 5UB, U.K. S. Ehrich Institut fur Seefischerei der Bundesforschungsanstalt fur Fischerei, Hamburg, Germany and P. A. Hulley South African Museum, Cape Town, South Africa The continental slope both truncates the distribution of the oceanic meso- and bathypelagic ichthyofauna and provides the headquarters of a diverse assemblage of demersal fishes. While demersal forms are well adapted to such an environment, the morphology of pelagic species differs conspicuously and seems better suited to an open ocean habitat. Submersible observations, together with a small body of near-bottom closing net data and records of pelagic fish in stomachs of demersal species, mainly constitute the scant knowledge of the interactions of these distinct faunal elements. In May, 1983, during cruise 58 of F.R.V. Walther Herwig (Institut fur Seefischerei, Hamburg) preliminary investigations were made into the swimming layers of the near-bottom ichthyofauna of the Rockall Trough (56°18'-44'N) using much larger nets than employed hitherto. Over a five-day period, five demersal trawls were made on the Feni Ridge and six on the Hebridean Terrace at approximately 200 m intervals from 200-1000 m soundings, using a 200 foot bottom trawl (200'BT—nominal mouth opening 22m x 6m headline height). In addition, nine Engels midwater trawl (1600PT—mouth opening 30mx20m high) collections were made in similar localities (Feni Ridge—four; Hebridean Terrace— five) and depths fished with the footrope (0) 3-18 (60) m above the sea bed, together with a set of mid-Trough samples from 100, 400, 700 and 1000 m depth available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0269727000014895 Downloaded from https://www.cambridge.org/core. IP address: 54.162.69.248, on 01 Jun 2020 at 20:09:24, subject to the Cambridge Core terms of use,