UNIVALVE SHELLS.
Patella. A conical univalve shell, with out a spire. Linneus had divided these shells into five sections; the labiated, the dentated, the mucronated, the en tire, and the perforated. Lamarck has divided this genus into five : 1. Patella, a shell of a shield or bonnet form, with out a spire, whole at the top, and simple within. 2. Crepidula, an oval shell, with an incomplete spire, inclined on the edge; the cavity separated into two, by a simple diaphragm. 3. Calyptni, a coni cal shell, whole at the point ; with a spiral diaphragm. 4. Fissurella, the shell pierced with a hole at the point S. Emarginula, a conical shell, summit in clined, concave beneath, and the poste rior edge slit or grooved.
Planospirites. A suborbicular flattish univalve, having in its inferior face, on one side, a cord-like border, turning back in spiral turns on the disk of the shell. The genus is formed by Lamarck on a fossil shell, found by Fait.* among the fossils of Maestricht ; but the figure has not yet been given Testacella. A univalve shell, in form of an oblique cone, the summit being ra ther spiral and the opening oval. This is the coveting of the posterior part of a long gasteropodia from the isle of Tene rife. This is therefore an animal be tween the slug and the snail.
Oscana. An oval, coriaceous, almost transparedt univalve shell without a spire. The shell of this genus, and of which one specks only is known, which is found ad hering to prawns, is in form similar to tlic the animal approaches to that of the Chiton.
Carinaria. A univalve shell, very thin ; its form a cone flattened on its sides ; its summit rolled spirally and very small; the back covered with a dentated keel ; the opening entire, oval, oblong, and con tracted towards the angle of the keel. Linnaus had placed this shell, which is exceedingly delicate, and as transparent as glass, among the Patella, by the name of Patella cristata ; but Dargenville, Mar tini, and Gmelin, have ranged it under the Argonauts by the name of Argonauta vitrea. Brugulere appears to have been disposed rather to have replaced it among the Patella : but Lamarck has thought it right to consider it as a species of a dis tinct genus.
Haliotis. A flattish ear-formed shell ; the spire much sunk ; the opening very large ; much longer than wide ; pierced with holes disposed in a line. No change is proposed in this genus of Linnxus by the French testaceologists.
Sigaretus. An oval, depressed, nearly ear-formed shell, with a short spiral co lumella ; the opening entire, very large, widened near the top of the right lip, and longer than wide. This shell had been placed by Linnzus among the Helices, under the name of Helix haliotoidez : and by Muller among the Huila, under the name of Huila velutina ; but Lamarck seems very probably to have disposed of it under a distinct intermediate genus be tween the Nerites and the ear.shells.
Stomatia. Is a genus which has been formed by Helblins and Lamarck from a shell, which has been placed under the genus Haliotis, but which wanted the holes which exist in the shells of that ge nus.
Argonauts. A very thin, single cham bered univalve shell : the spire concealed in the internal part of the shell.
Concholepas. An oval univalve, con vex in its superior part, with its summit obliquely inclined upon the left edge ; the cavity simple ; two teeth and a sinus at the base of the right edge. Dargen ville and others had placed the shell of this genus among the Patella ; but Bru gulere, having seen several with tendin ous opercula, disposed them under the genus Buccinum. Lamarck has, how ever, thought fit to consider it as forming a genus connecting the Patellae with the ether spire valved shells.
Nerita,A semiglobular univalve, flat tish beneath, not umbilicated at the spire, the opening semicircular, the columella or partition nearly transverse. Lamarck has retained in this genus only the im perforated Nerites ; the others he trans fers to the next genus The Nerites have not only no umbilicus, but no true colu mella, having in its place a simple parti tion, which is flat, thin, and longitudinal, originating in the groove of the first spire, and generally dentated.