BULLAS. 147 
GENUS PHILINE. 
In this genus the shell is thin, fragile, and 
colourless, of a broad rounded outline, with the 
aperture very wide, and a small spire, frequently 
concealed. The animal is proportionally large, 
slug-like, and slimy, with the power of secreting 
and of throwing off an adhesive mucus in copious 
abundance. ‘he shell is partially covered by the 
mouth, the side lobes of which are well developed. 
The head disk is obscurely four-sided, without 
eyes or distinct tentacles. 
Of the six species of this genus which are found 
in the British seas, the largest . 
is P. aperta, the Gaping Bulla. 
It is an unpleasing, almost shape- 
less slug, very soft and slimy to 
the touch, of an opaque white 
hue, sometimes tinged with pale 
orange. Looked at from above, 
it appears to be composed of four 
portions,—the square head-disk, 
the body partly enclosing the 
shell, and the lobes or wings of 
the mantle turned up on each 
side and investing it. It is 
usually about an inch and a THe Garine suina. 
quarter in length, but individuals are found of a 
larger size. 
The shell, on being dislodged, is transparent and 
colourless, but on drying loses somewhat of its 
clearness, and becomes of a lustrous white hue. Its 
surface is smooth, except for the concentric lines, 
which mark its progressive increase. The aperture 
