CONCHIEERA. 
454 
** Shells with one or two lateral teeth. 
Genus 32.—DON AX.— Linnceus. 
Generic Character. —Transverse, equivalve, inequilateral; 
with the anterior side very short and obtuse; two primary teeth, 
in one or both valves; and one or two lateral teeth, more or less 
apart; ligament external, short, inserted at the posterior im¬ 
pression. 
Donax trunculus. — The Truncated Don ax. 
Plate XC. fig. 5. 
Oblong, glossy, finely striated, and radiated longitudinally; 
transversely banded with purple ; white, and clouded with pur¬ 
ple within ; margin crenulated. One inch and a quarter broad. 
Inhabits the seas of Europe. 
This genus consists of two sections :—* Shells with the mar¬ 
gins entire.—** Margins crenated. 
Genus 33.—LUCINA.— Lamarck. 
Generic Character. —Suborbicular, inequilateral; beaks small, 
pointed, and oblique ; hinge variable, sometimes with two diver¬ 
gent teeth, one of which is bifid, but changing with age; two 
lateral teeth, the intermediate one obsolete; the posterior near¬ 
est the primary ones; two distinct muscular impressions, the 
posterior one prolonged. 
Lucina undata. —The Waved Lucina. 
Plate XC. fig. 7. 
Orbicular, thin, convex, undulated with fine irregular striae; 
pale straw-coloured yellow, and white in the inside; margin 
glossy and plain. Inhabits the British seas. 
Genus 34.—MYSIA.— Leach. 
Generic Character. — Suborbicular, inequilateral; beaks small, 
pointed, and very slightly turned to one side; hinge with two 
primary teeth, joined at their base and divergent, behind which 
is an oblique descending cavity; with one strong muscular im¬ 
pression in each valve ; margin thin and entire ; ligament exte¬ 
rior. 
