lished on their distribution. Valuable materials have, however, been collected in the larger works of Montagu, Turton, and Fleming, and in many essays on local faunæ, among which, the Report of Mr. W. Thompson 'On the Irish Invertebrata,' published in the Transactions of the British Association for 1843, and prepared at the request of that body, is by far the most important. The following sketch of the distribution of marine Mollusca on the British shores, is offered as a brief summary of the results, chiefly of my own obsenrations.
I. In the southern part of the British Channel, we find certain species which haye there the northernmost limits of their range. Such are Haliotis tuberculata, which, abundant in the Channel Isles, is not indigenous on our own shores, Emarginula rosea, occasionally taken on the south coast of England, but frequent on the coast of Guernsey, Truncatella Montagui, Rissoa Bryerea, denticulata and calathisca, Calyptrea sinensis, Donax complanata, Lucina pisiformis, Galeomma Turtoni, Pandora rostrata, and Lithodomus lithophagus. These species mark the bounds of a fauna which can scarcely be regarded as within our limits.
II. Some of them, howeyer, are occasionally found alive on our southern shores, and on the south and south-west of Ireland, associated with a number of species which constitute a well-marked South British type. Such are Avicula atlantica, Modiola Gibsii, Venus verrucosa, aurea and chione, Venerupis irus, Arca lactea, Cardium tuberculatum, Pholas dactylus and lamellata, Volva patula, Pleurotoma gracilis, Trochus exasperatus, striatus and crassus, Adeorbis subcarinatus, Rissoa striatula and auricularis, and Pollia minima. This fauna stretches far up on the coast of Ireland, occupies St. George's Channel, having its northern limits about the line of Cardigan Bay, and is generally distributed through the English Channel, even to the entrance of the German Ocean.
III. There are certain species very generally diffused throughout the seas and shores of the British Isles, and which range generally through the European Seas, or at least along the coasts of Western Europe, from Norway to the south of Spain. Such constitute an European type. Such are: Turritella terebra, many Rissoæ (as, R. striata, cingilla, parva, interrupta, ventricosa, fulva), Odostomia plicata, Trochus magus, ziziphinus, tumidus, cinerarius, several Pleurotomæ, Aporrhais pespelecani, Cypræa Europæa, Tornatella fasciata, Natica Alderi, Dentalium entalis, Patella vulgata, Emarginula fissura, Chiton fascicularis, Capulus hungaricus, Ostrea edulis? Pecten opercularis, Nucula nuclea, Modiola marmorata, Cardium edule, lævigatum and echinatum, Donax trunculus, Tellina donacina, tenuis, and fabula, Abra Boysii, Mactra stultorum, Kellia suborbicularis, Artemis exoleta and lincta, Venus ovata, fasciata, and gallina, Pullastra virginea, Corbula nucleus, and Psammobia tellinella.
