PULMONATA. 113 
or three folds upon the columella; outer lip sometimes simple and sharp, sometimes 
thickened, and occasionally denticulated within. 
The genus Awricula, as described by Lamarck, was confined to land shells; and 
that of Conovulus, proposed by him for certain shells which he considered to be 
fluviatile, he afterwards suppressed under the impression that they also were land 
shells. The animals which have been referred to the genus Avricula have, however, 
various habitats: some are terrestrial; others live in ponds or fresh-water marshes ; 
and others, again, are inhabitants of the sea, or are found in brackish water near the 
mouths of rivers, or in salt-water marshes. Some of these groups are distinguished 
by peculiarities in the animals or their shells ; and they, accordingly have been with- 
drawn from Auricu/a as distinct genera. The present genus, which corresponds with 
Lamarck’s Conovulus, was first separated by Montfort for a shell from the shores 
of Cayenne. The animal resembles that of Zzmnea; the head is proboscidiform, 
notched in front, and furnished with two filiform contractile tentacles, slightly annu- 
lated, and oculated at their mner bases; the foot is obovate and obtuse before and 
behind; the mantle united to the neck, with the exception of a perforation at the 
junction of the outer and inner lips. The J/e/ampodes are strictly marine animals, 
although they are frequently found in brackish waters near the mouths of rivers or salt- 
water marshes; they are capable of living out of water for a long period, and Mr. 
Lowe, in fact, characterises them as amphibious. 
The living species are not numerous; three are inhabitants of our own shores; 
the others are found principally in warm climates. The fossil species hitherto described 
are from the Eocene and later formations, and have for the most part been referred 
to Auricula. 
The peculiarity, observed by Montagu in Avricula denticulata, of the columella not 
extending further than the upper part of the body whorl, is stated by Mr. Gray to be 
common to most species in the family; and to be caused generally by the animal 
absorbing the septa which separate the upper whorls, and thus converting the spire 
into a single cavity, as it enlarges the shell at the edges of the aperture. 
No. 65. MELAMpus TRIDENTATUs. J. HL. Edwards. Tab. X, fig. 4 a—é. 
M. testé ovato-ventricosd, crassd, levi; spird conico-depressé, apice obtusiusculo ; 
anfractibus sex vel septem, sub-cylindraceis, superne depressiusculis: aperturd auriformi, 
angustd, labro interne incrassato, antice reflexo: columella marginatd, tridentata. 
A thick, smooth, ovate, ventricose shell, with a short conical spire and a bluntish 
apex; volutions six or seven, sub-cylindrical, and somewhat depressed round the 
suture; the aperture long, narrow, and ear-shaped ; the outer lip rather enlarged and 
inflected in front, and thickened internally, presenting an elevated sharpish ridge, which 
extends from a little above the middle of the whorl to the columellar lip. The colu- 
216) 
