BIVALVES. =F 35) 
itself with the shell immersed and inverted, by 
olutinous 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 im 
number (each gill containmg not more than 
about six), and of different sizes, the largest va- 
rying from one-eighth to one-fourth the length 
of the parent. 
The larve of a fluke (Amplhistoma subclava- 
tum) 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 Ter- 
tiary species. 
Cycias pisipiorpes (Pl. IIT. ie 9) is a recent 
addition to science; it was Hesnverid, 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 OC. cornea by its subtri- 
angular shell, which is somewhat produced behind 
and shghtly wrinkled concentrically. 
ee 
