CONCHOLOGY: 
fixed by an operculum or tendon. Hinge with- 
out teeth. Ligament placed transversely under 
the beak. 
Includes.the whole of this family. 
44. Pecten. Shell free or fixed, orbicular or ob- 
long, transversely dilated into auricles at the base; 
the beaks equal and close together. Hinge without 
teeth, with an internal triangular cavity. 
Includes the whoie of the Scallop tribe. 
45, Discina, Shell inequivalve, roundish—oval, 
flattish, and fixed; each valve furnished with an 
orbicular- central disk: the disk of the upper 
_valve papillary near the middle of the under 
valve divided by a_ transverse cleft. Hinge 
indistinct. 
Includes the Patella distorta of Montagu. 
46. Mya. Shell transverse, equivalve, openat the 
sides. Hinge with a single elevated transversely 
dilated tooth in the left valve, and none in the 
right : lateral teeth none. 
Includes M. truncata, arenaria, and ovalis of 
Turton’s Bivalves. 
47, Sphenia, Shell transverse, inequivalve, open 
at the anterior end. Hinge of the left valve with 
an elevated transversely dilated tooth, of the right 
valve with a concave tooth and small. denticle; 
lateral teeth none. 
Includes Sph. Binghami and Swainsoni of 
Turton’s Bivaives. 
48, Lutrarza, Shelltransverse, oblong, equivalve, 
open at both the sides. Hinge with a spoons 
