Since the appearance of Johnston's Catalogue of the British Non-parasitical Worms in the Collection of the British Museum—a work which although not published until 1865 had been completed some ten years earlier and consequently embodies observations made more than half a century ago—the Hirudinea of the British Islands have been largely neglected. Apart from this the interest now being taken in leeches by students of their protozoan parasites and the absence of any recent work upon this group of our fauna seems sufficient apology for the revised descriptive catalogue attempted in the following pages.
