many of the forms common to the British and Mediterranean Seas, are mingled in their course with forms characteristic of the Celtic, Boreal, and sub-Arctic regions; and nothing but the most minute examination and the active employment of the dredge, and registering of its contents, could have cleared up the confusion which this peculiarity in the distribution of the fauna of our western shores, bordering the Atlantic, threatened to introduce into all our calculations.
This portion of our fauna, which for convenience I will term the Atlantic type, to distinguish it from the Oceanic, we see exemplified in such species as, Bulla cranchii, Eulima polita, Eulima subulata, Littorina cœrulecens, Rissoa cimex, R. costata, Scalaria Treveliana, and clathratulus, Cerithium lima, Triphoris adversus, Pleurotoma attenuata, linearis, purpurea, gracilis, Erato lævis, Terebratula caput serpentis? Pecten lævis, Lima tenera? Lima subauriculata, Arca tetragona, Cardium elongatum? Lucina spinifera, Circe minima, Pullastra decussata, Solenecurtus candidus, and antiquattis, Psammobia florida (vespertina, Turt. non Lam.) and Gastrochæna pholadia.
VII. On the same coasts with these species are taken the mollusks of an Oceanic type, mostly occasionally visitors drifted hither by storms from the west and south. Such are Spirula Peronii, which has several times been cast up on the west coast of Ireland, Ianthina communis, nitens, and exigua, Hyalæa trispinosa, and possibly Peracle Flemingii. With these we may expect some day to find other species of Pteropoda. The various species of Anatifa among the cirrhipeds, and of Velella and Diphyes among our Medusæ, included in our fauna, are members of the same type.
VIII. The coasts of Scotland, and the neighbouring parts of England and Ireland furnish the cabinets of conchologists with many species which are very rare or almost unknown on the English shores. Some of these are confined to the east coast, some to the west, but the greater number are common to both. Such are, Pecten niveus, nebulosus and striatus, Nucula tenuis, minuta and pygmæa, Crenella decussata, Modiola nigra, Cardium Löveni, Abra intermedia, Astarte elliptica and compressa, Cyprina islandica—found everywhere on our shores, but abundant only in the north—several species of Neœra, Panopæa arctica, Margarita communis and striata, Trichotropis borealis, Fusus Barvicensis, Bamfius, and Norvegicus, Velutina lævigata and ovata, Natica helicoides, Lottia ancyloides, testudinaria and fulva, Emarginula crassa, Cemoria noachina, Chiton Hanleyi, Crania Norvegica, and Terebratula caput serpentis. Most of these species are found also on the Scandinavian shores, and several of them are common to the North American and North European Seas. They constitnte my Boreal type, the province of which extends northwards, from the northern shores of the Isle of Man and Ireland, on
