JEFFREYSIA. 151 



JEFFREYSIA. Alder. 



"Shell spiral, conical or subglobose, thin, transparent ; 

 aperture ovate, rounded below, with the peristome thin 

 and entire. Operculum horny, thin, imperfectly ovate, 

 nearly straight on one side ; not spiral, but showing faint 

 concentric lines of growth from a lateral nucleus. It is 

 strengthened internally, on the side next the columella 

 of the shell, by a rib with a branch towards the centre of 

 the operculum : from this rib rises a strong projecting 

 plate, set at right angles to the opercular disc. 



" Animal with four flattish tentacles ; the upper pair 

 moderately long, the lower pair rather shorter, and 

 spreading out broad at the base so as to unite with the 

 outline of the head. Eyes placed on the back of the 

 animal, a considerable distance behind the tentacles. 

 They are large and prominent. Operculigerous lobe small 

 and rounded, without filaments or prolonged appendages. 

 Foot oblong, notched and bilobed in front, with a groove 

 down the centre, and slightly rounded behind. The 

 armature of the tongue consists of a broad crenulated 

 central tooth, flanked by two lateral ones on each side : — 

 the first broad and crenulated, the exterior one small and 

 hooked. 



" There is no character in the shell of this curious genus 

 by which it can be distinguished from Bissoa. In the 

 only two species yet known, both minute, the shell is 

 transparent, and from the remarkable position of the eyes 

 of the animal, so far behind the usual place, and constantly 

 within the shell, its transparency is probably a constant 

 character of the genus, being necessary for the exercise of 



