Xviii INTRODUCTION. 



III. The European type, represented by species that 

 are equally diffused and abundant in most parts of the 

 British Seas, and which at the same time have a wide 

 range along the shores of Europe, although none of them 

 cross the Atlantic. To this section belong, among others, 

 the Aporrhais pes-pelecani, A rtemis exoleta and lincta, Car- 

 dium echinatum, edule, fasciatum and Norvegicum, Chiton 

 fascicularis, Gorhula nucleus^ Cylichna cylindracea, Cypraa 

 Europeea^ Donax anatinus,Emarginula reticulata, Kellia sith- 

 orbicularis, Lucinopsis undata, Lutraria elliptica, Mactra 

 solida, stultorum and suhtrimcata, Mangelia linearis, Nassa 

 reticulata, Natica nitida, Nucula nucleus, Patella md- 

 gata, Pecten opercularis and pusio, Pectunculus glycimeris, 

 Pileopsis Hungaricus, Psammohia Ferroensis, Solen siliqua, 

 ^yndosmya alba. Tapes virginea, Tellina Donacina, tenuis 

 and solidula, Tornatella fasciata, Trochus cinerarius, tu- 

 midus and zizypliinus, Turritella communis, Venus fasciata, 

 ovata and striatula. Several of our Nudibranchiate Mol- 

 lusks, and some Ascidians, probably belong to this group. 

 Many of the above-cited species are remarkably prolific, 

 and the individuals of them often constitute a large pro- 

 portion of the contents of the dredge, or are to be gathered 

 numerously on the shore. 



IV. Along with the last, and most of them as plentiful, 

 are the members of the Celtic type, a group especially 

 characteristic of our area. This assemblage consists of 

 species that are essentially Atlantic. They are most pro- 

 lific and at home within the Celtic province, of which the 

 British Islands constitute an important portion. They 

 have a tendency to diffuse themselves rather northwards 

 than southwards, multiplying rather in the boreal than in the 

 Lusitanian province. Many of them are of ancient origin, 

 and well known in the fossil state. As examples we may 



