itself with the shell immersed and inverted, by glutinous threads, which are spun by the foot, or it may even be observed gliding along the surface of the water in an inverted position. It is very active, and climbs the submerged plants with great facility, among which it is usually found; it can suspend itself by its glutinous threads, which are of the nature of a byssus, as in the Driessena and Mytilus. It thrives well and breeds in confinement; the fry are hatched in the gills, are but few in number (each gill containing not more than about six), and of different sizes, the largest varying from one-eighth to one-fourth the length of the parent. The larvæ of a fluke (Amphistoma subclavatum) have been found on the surface of the body of this and other species of Cyclas, as also on the coil-shells (Planorbis). It is a newer Tertiary species. CYCLAS PISIDIOIDES (Pl. III., fig. 9) is a recent addition to science; it was discovered, in 1856, in the Paddington Canal, near Kensal Green, London. It has much the appearance of a large Pisidium; hence its specific name. The adult shells are six lines long, five wide, and four thick. It is distinguished from C. cornea by its subtriangular shell, which is somewhat produced behind and slightly wrinkled concentrically. The same locality supplied, at the same time, a species new to Britain, CYCLAS OVALIS-(the Oval Cyclas) (Pl. III., fig. 10)-is a species intermediate in size and form between C. rivicola and C. cornea. Average-sized specimens measure half an inch long, a quarter of an inch thick, and three-eighths wide. From C. rivicola it is distinguished by its oblong shape, its pale-drab colour, and fainter concentric striæ, and more markedly by its straight hinge-line. It has since been found. in the Surrey Canal, at Exmouth, and in Lancashire. It occurs in marshes in the North of France. CYCLAS LACUSTRIS-(the Capped Cyclas) (Pl. III., fig. 12).—The shell of this species contrasts strongly with those of the other Cyclads, in its sub-rhombic form, much compressed, thin, of a yellowish-white colour; in the prominent umbones, which are narrow, and projecting like little caps, from which latter character it has also received the specific name calyculata. The shell is small, delicate, and shining, four lines long, three wide, and one and a half thick. From the extreme thinness and semitransparency of the shell, the young, the lamellated gills, and the pulsating heart may be easily seen within. C. lacustris has much the same habits as C. cornea, but exhibits greater activity than it does. We quote a writer in the Zoologist, who gives in a few words the performances of this bivalve in confinement. "When I first put them (C. lacustris) into water they immediately began to climb the sides of the glass. One of them also commenced crawling on the under surface of the water. Its foot was now spread out very widely, and while preparing for its exploit, it was apparently kept near the surface by a minute thread fastened to the sides of the glass. When it had left the side, its foot appeared to be depressed in the middle, so as to act as a kind of boat. I shook the tumbler, so as to fill the little vessel with water; but to my surprise it sunk, not suddenly but gradually, as if it were lowering itself by a thread attached to the surface of the water. They also appeared to give out a quantity of glutinous matter wherever they went, so much, that in about half an hour seven or eight were entangled and tied together by each other's trailing threads." The capped Cycle inhabits ponds, canals, ditches, and lakes in the South and centre of England, becoming rare in the North; it is absent in Scotland, and is rare and local in Ireland, having been observed only near Dublin, Dundalk, Youghal, and Cork. |