THE EUROPEAN SEAS. 



87 



into several sub-regions. The first and uppermost 

 is that of Littorinae, where these mollusks are asso- 

 ciated with bivalves of the genus Mya, and with 

 worms of the genera Nereis, Spio, and Arenicola (lug- 

 worms). The second is the sub-region of Mytilus 

 edulis, the common mussel. It corresponds to the 

 sea-wrack's domain. Here we find the Altera bul- 

 lata, the A scidia intestinalis, the common sea-urchin 

 (Echinus sphazra), and the harry-crab (Carcinus 

 moenas). The third sub-region is that of the little 

 whelk, Nassa reticulata, which, with the small bi- 

 valve, Corbula nucleus, prevails here. Several fishes 

 are dwellers here, as Spinachea vulgaris, Cottus scor- 

 pius, the gunnel, the viviparous blenny, the fluke, 

 and the sand-eel. Certain shell-fish, normally fresh- 

 water species, intrude under Baltic conditions here, 

 such as Limnceus Balticus (i. e. a var. of L. pereger), 

 and Neritina Baltica (i.e. a var. of N. fluviatilis). 

 The second animal province is the Regio Gymno- 

 branchiorum. It corresponds with the Laminarian 

 and Rhodospermean plant belts. It is but partial 

 in this locality. Its inhabitants are often remark- 

 able for colour and variety. Among mollusks there 

 are Limpets, Chitons, Ascidece and nudibranchs; 

 among Crustacea, Caprellidce and Fycnogonidce. 

 Most of its characteristic inhabitants are soft, or 

 at least not strongly protected. The third, and 

 lowest animal province, is the Regio Ruccinoi- 

 dearum ; occupying the deeper part of the straits, 

 mostly on a muddy bottom. Its population are 



