Page:Natural History, Mollusca.djvu/117

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105
NAKED-GILLED MOLLUSKS.

in seizing and securing its prey. It is covered with numerous transverse plates, armed with spines or teeth directed backwards. These teeth differ in number and in form; those of Eolis papillosa, figured above, are very numerous and minute, being not more than one-sixth part of the thickness of a human hair. Their arrangement is in transverse arched rows, but in E. coronata, there is one large central tooth on each plate with denticulated sides; and in E. alba, a central tooth only, without denticulations.


Family Dorididæ.

The members of this extensive family are characterised by having the anal orifice placed in the medial line of the back, towards the hinder part, and the respiratory organs arranged around it in a more or less complete circle of leaf-like plumes, so as to resemble the petals of a beautiful flower. The mouth is a small conical proboscis placed under the front edge of the mantle, where this latter organ is distinct, and sometimes guarded by two simple tentacles; another pair of tentacles is placed on the front part of the back. These are peculiar in their structure, being beset with numerous narrow plates, arranged diagonally, parallel to each other. These tentacles, for the most part, are capable of being withdrawn into proper cavities, the edges of which, in many cases, are raised into tubular sheaths to protect them.

The Dorididæ are found on the shores of every sea. Many species are common on our own coasts, crawling on sea-weeds, or concealed beneath stones between tide-marks; some kinds, however, confine