458 
CONCHIFERA. 
purple. Three quarters of an inch broad. Inhabits the British 
seas. 
Genus 43.—P E T RIC O L A. — Lamarck. 
Generic Character. —Subtrigonal, transverse, inequilateral ; 
posterior side rounded, and the anterior attenuated, and slightly 
gaping; hinge with two teeth in each valve, or in one valve 
only. 
Petricola pholadiformis .— The Pholas-Shaped Petricola. 
Plate XC. fig. 17. 
Transversely elongated; umbones very small; with trans¬ 
verse, rough, prickly striae; posterior side extremely short. 
Three inches long. Inhabits the Australian seas. 
Genus 44.—SAXICAVA.— Lamarck. 
Generic Character. —Inequilateral and transverse; the ante¬ 
rior upper margin gaping; hinge nearly without teeth ; ligament 
external. 
Saxicava prcecisa _The Abbreviated Saxicava. 
Plate XC. fig. 18. 
Oblong, wrinkled, one valve larger than the other, truncated 
at the posterior end; of a pale horn-colour. Three quarters of 
an inch broad. Inhabits the British seas. 
TRIBE III.-CORBULACEA. 
Inequivalve shells, with an interior ligament; one of the 
beaks always projecting beyond the other. 
Genus 45. —PANDORA.— Lamarck. 
Generic Character. —Shell regular, inequivalve, inequilateral, 
and transversely oblong; upper valve flattened, and the under 
one convex; hinge with two oblong diverging cardinal teeth, in 
the upper valve, and the other valve with two oblong grooves ; 
ligament external. 
Pandora rostrata. — The Beaked Pandora. 
Plate XC. fig. 19. 
White, oblong, much produced towards the beak; one valve 
