19(X Dr. Turton on the Genus Lacuna. 



Art. XVIII. On the Genus Lacuna. Bj/ Dr. Turton. 



In the Conchological Dictionary the subjects of this family 

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

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

 they so materially differ in many circumstances, as to form of 

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

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

 Their essential differences 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 Eburtia^ 

 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, epidertnide induta. Aper- 

 tura integra, rotundato-ovata ; labiis superne disjundis. 

 Columella plamilata, sulco longitudinali superne in umbi- 

 licum desinentc. 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 M'hich 

 terminates at the upper end in an umbilicus. Operculum 

 horny. 



* Spira laieruli, vix pj-oducid. 

 Spire lateral, very slightly produced. 



1, L. pallidula, icstd semiovatA, Jlavesccnti-conicd : spird trun- 

 cald : aperturd dilaiafd, subangulatd. 



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



dilated, somewhat angular. 

 NcritapalUdula. Da Costa, t. 4. f. 4. Donovan, t. 16. f. I. 

 Montagu, p. 468. 



