GASTEROPODA. Ill 



Genus 8. — BULLA. — LinncBus. 



Generic Character. — Body oblong-ovate, slightly convex; 

 divided into two transverse portions above, and having the 

 mantle slightly folded posteriorly ; no apparent tentacula ; 

 branchiae on the fore part of the back, and covered ; anal 

 opening placed in the right side. The posterior part of the 

 body covered by an involute shell, with neither pillar nor 

 spire ; aperture extending the whole length of the shell. 



Bulla lignaria — The Wood-like Bulla. Plate XIV. 

 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, 

 and those of Europe generally. 



Genus d.—BJ3lA,Mk.— Lamarck. 



Generic Character. — Body ovate-oblong, somewhat con- 

 vex above, and divided transversely into two parts; the 

 lateral lobes of the foot thickened and bent upwards; head 

 indistinct, and without tentacula ; branchiae placed on the 

 back. Shell concealed in the mantle; thin, somewhat in- 

 volute on one side, and destitute of a columella or spire ; 

 aperture large and wide. 



Bullcea aptrta The Open Bull^a. Plate XIV. fig, 



23. Suborbicular, pellucid, white, faintly striated, and 

 slightly wrinkled ; almost entirely open. Half an inch long. 

 Inhabits the British seas, and those of Europe generally. 



Genus \0.—RET\JSA.—Brow7i. 



Generic Character. — Animal unknown. Shell small, 

 oblong-ovate, spiral, outer lip nearly the whole length of 

 the body, and entire ; spire very short, volutions promi- 

 nent. 



Retusa plicata. — The Plaited Retusa. Plate XIV. 

 fig. 27. White, opaque, subcylindrical ; spire produced ; 

 aperture elongated, straitened at top; two transverse plaits, 



k2 



