Mr. C. Spence Bate on British Edriophthalmous Crustacea. 135 XII. — A Synopsis of the British Edriophthalmous Crustacea. By C. Spence Bate, F.L.S. &c. — Part I. Amphipoda*. Class CRUSTACEA. Legion II. Edriophthalma. Order I. AMPHIPODA. Group A. NORMALIA. Division I. Gammarina. Subdivision I. VAGANTIA. Do not construct abodes to dwell in. Tribe I. Saltatoria. Mode of progression out of the water is by leaps. Family I. Orchestidse. The upper antenna shorter than the lower. The coxse well developed ; the posterior pleopoda short and robust, the last being single. Genus 1. ORCHESTIAf. Upper antenna rudimentary ; the lower with the basal joints absorbed within the facial wall of the cephalic segment. Olfactory spine absent. The second pair of feet subcheliform. Subgenus 1. Talitrus, Latr., Bosc, Leach. First pair of feet simple in both sexes. 1. T. Locusta, Latr. Second pair of feet feeble, terminating in a subcheliform hand, and folded beneath the body; the dactylos small, and articulating remote from the apex of the propodos. The last pair of the posterior pleopoda rudimentary. The telson obsolete. Sandy shores all round Europe, at high-water mark. Subgenus 2. Talorchestia, Dana. First pair of feet simple in female only. [Of this subgenus there is no British species known.] * The classification adopted in this Synopsis is the result of the united labours of Mr. Westwood and the author ; it is based on the structure and the habits of the animals as far as known. The characters given are only those which more immediately strike the observer. Many of the terms employed are new ; they are explained at the end of this paper. t The classification adopted in this genus is that given by Dana, and the result of his discovery of the intermediate form of Talorchestia.