On passing the interesting group of islands in the Gulf of St. Lawrence, known as the Magdalens, the observer is struck with their beautiful and picturesque appearance, which is suddenly presented to his view. The cliffs, which vary in height, present equally various colours, in which the shades of red predominate; these, contrasted with the yellow of the sand-bars, and the green pastures of the hill-sides, the darker green of the spruce trees, and the blue of sea and sky, produce an effect, as Captain Bayfield describes, extremely beautiful, and one which distinguishes these islands from anything else in the Gulf. Such an agreeable picture it has been my own good fortune to witness and admire. The striking feature in their formation is the dome-shaped hills rising in the centre of the group, and attaining a height of from two hundred to five hundred and eighty feet. They are composed of the Triassic or New Red Sandstone formation, which forms their base, being surmounted or topped by masses of trap rocks.

This species appears to vary somewhat in appearance, but is usually transversely semi-cylindrical, the hinge-line being at the same time the widest portion of the shell. The ventral valve is very much vaulted, and usually longitudinally divided by a median depression or sinus of variable depth. The beak is small, and does not overlie the hinge-line, while the ears are of moderate dimensions and clearly defined. Exteriorly the surface is ornamented with numerous longitudinal ribs, which increase in number by means of occasional intercalations; certain ribs will also disappear before having attained the margin; while again two will sometimes unite, so as to constitute but a single rib. The costæ are very often of unequal width, rounded, or flattened, and sometimes will rapidly increase in width as they extend towards the margin: concentric wrinkles are also observable upon the auriculate portions of the valve, and a row of long tubular spines may be seen close to the cardinal edge, as well as upon the lateral portions of the beak; spines of smaller proportions project likewise here and there from the ribs themselves, while the longitudinal costæ are closely intersected or decussated to some distance from the extremity of the beak by numerous undulating concentric lines.