wonderful. Yet, although essentially a borer, and possessed of such singular powers, it sometimes is found perfectly free, and frequently is discovered merely lying in rocky crevices.
When a piece of rock is thickly studded with the Saxicava, it presents a curious and rather pretty appearance. The whole surface of the rock is covered with very small crimson projections, which, when touched, instantly vanish into the stone, leaving only the little holes through which they had protruded. These are the ends of the siphons which the Saxicava protrudes into the water, and by means of which it both procures nourishment and is enabled to respire. The general colour of the animal is yellow, which deepens into orange upon the siphons, becoming quite red at their extremities.
At fig. 8 of Plate I. is shown a shell which is closely allied to the preceding species, and which cannot be distinguished except by very careful eyes. This is called Saxicava arctica; and although in the figure it is easily distinguishable from the species which is shown at fig. 7, there are really few shells which are more difficult to identify. If the shells retained the same form throughout life, there would be no difficulty in separating them, inasmuch as the sharp spinous scales of the present species afford a boldly distinguishing character ; but as both species change their shape in the course of their lives, as the young specimen of Saxicava rugosa possesses the same spinous scales as the adult arctica, and as both species lose these scales when old, a skilful eye is needful for the detection of any permanent characteristics. Such, however, may be found in the beak of the shell, i. c., the part immediately above the hinge, and in the front edge of the shell; the former being sharp and leaning forward, and the latter being rather sharp and pointed, instead of being broad and rounded, as in the last species.
The colour of the animal is yellowish, and the siphons are of any shade of orange, rose, or brown. It
