t90 Dr. Turtoti on the Genus Lacuna* 



Art. XVIII. On the Genus Lacuna, By Dr. TuRxoili 



In the Conchological Dictionary the subjects of this family 

 •were first collected together, and formed a division of the genus 

 ^urbo. From the Turbo however, as it is defined by Lamarck, 

 they so materially diff'er in many circumstances, as to form of 

 themselves a truly new and characteristic genus. None of them, 

 we believe, were known to Linne, or the above illustrious author. 

 Their essential diff*erences from the Turbo are, 1. They are of a 

 thin, and generally of a semi-transparent substance; 2. They 

 are clothed with an epidermis or thin outer skin ; 3. There is a 

 groove along the pillar, terminating in a cavity at the upper end. 

 This last mark is to be found only in this and the genus Eburna, 

 which are of entirely distinct divisions ; the Eburna is sarcopha- 

 gous, and marked by a notch or reflexure at the base of the 

 aperture. The Lacuna is phytophagous, with the base of the 

 aperture entire. All the species are found feeding on Fuci. 



Testa tenuis^ conoidea vel subglobosa, epidermide induta, Aper- 

 tura Integra J rotundato-ovata ; labiis superne disjunctis* 

 Columella planulata^ sulco longitudlnali superne in umbi" 

 licum desinente. Operculum corneum. 



Shell thin, conoid or somewhat globular, clothed with an epider- 

 mis. Aperture entire, roundish or oval, with the lips disunited 

 at top. Pillar flattened, with a longitudinal groove which 

 terminates at the upper end in an umbilicus. Operculum 

 horny. 



* Spira laterally vix productd. 

 Spire lateral, very slightly produced. 



1. L. pallidula, testa semiovatd, Jlavescenti-cornea : spirA trun^ 

 cata : aperturd dilatatd, subangulatd. 



Shell semioval, yellowish horn-colour : spire truncate : aperture 



dilated, somewhat angular. 

 Nerita pallidula. Da Costa, t. 4. f. 4. Donovan, t. 16. f. I. 

 Montagu, p. 468. 



