MOLLUSCA. 
419 
Bulla lignaria. — The Wood-like Bulla. 
Plate LXXXVII. fig. 25. 
Narrowed towards the top, where it is slightly umbilicated ; 
yellowish-brown, with numerous transverse pale striae. Two 
inches long. Inhabits the British seas. 
Genus 9.—BULLAE A.— Lamarck. 
Generic Characfer. —Body ovate-oblong, somewhat convex 
above, and divided transversely into two parts ; the lateral lobes 
of the foot thickened and retrousse; head indistinct, and with¬ 
out tentacula; branchiae placed on the back.—Shell concealed 
in the mantle ; thin, somewhat involute on one side, and desti¬ 
tute of a columella or spire ; aperture large and wide. 
Bullcea aperta. — The Open Bullae a. 
Plate LXXXVII. fig. 23. 
Suborbicular, pellucid, white, faintly striated, and slightly 
wrinkled; almost entirely open. Half an inch long. Inhabits 
the British seas. 
Genus 10.— RETUSA.— Brown. 
Generic Character .—Animal unknown. — Shell small, oblong- 
ovate, spiral, outer lip nearly the whole length of the body, and 
entire ; spire very short, volutions prominent. 
Retusa plicat.a — The Plaited Retusa. 
Plate LXXXVII. fig. 27. 
White, opaque, subcylindrical; spire produced; aperture elon¬ 
gated, straitened at top; two transverse plaits, and several ob¬ 
lique ones, at the base of the columella ; outer lip thin, slightly 
inflected. One-third of an inch long. Inhabits the sea at 
Dunbar. 
Genus 11—AKER A.— Brown. 
Generic Character .—Animal not described.—Shell elastic, 
convoluted; apex obtuse, canaliculated, the volutions even with 
the body; aperture wide at the base, contracted at top, and ex¬ 
tending the whole length of the body ;* columella visible to the 
end. 
