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Shaped like a boat; (Bot.) elongated and having the upper surface decidedly concave, as the glumes of many grasses.

Having the middle lower than the border; concave. [Obs.] If the seal be depress or hollow. Hammond.

Concave on the upper side; -- said of a leaf whose disk is lower than the border.

ored dispersion produced by a single object lens of crown glass is corrected by a smaller concave lens, or combination of lenses, of high dispersive power, placed at a distance in the narrower part of the converging cone of rays, usually near the middle of the tube.

g the spiral curve of the volute. Gwilt. -- Diminishing rule (Arch.), a board cut with a concave edge, for fixing the entasis and curvature of a shaft. -- Diminishing stile (Arch.), a stile which is narrower in one part than in another, as in many glazed doors.

The state of being concave, or like a dish, or the degree of such concavity; as, the dish of a wheel.

Dish-shaped; concave.

To remove the epidermis of (a skin) with a concave knife, blunt in its middle part, -- as in making chamois leather.

Indented with small concave curves, as the edge of a bordure, bend, or the like.

A concave filling in of a reëntrant angle where two surfaces meet, forming a rounded corner.

n wheel. -- Spur gearing, gearing in which the teeth or cogs are ranged round either the concave or the convex surface (properly the latter) of a cylindrical wheel; -- for transmitting motion between parallel shafts, etc.

t an axis, fulcra on the fins, and a bony skeleton, with the vertebræ convex in front and concave behind, forming a ball and socket joint. See Ganoidel.

A concave molding; a cavetto. Gwilt.

elescope, named from Prof. James Gregory, of Edinburgh, who perfected it in 1663. A small concave mirror in the axis of this telescope, having its focus coincident with that of the large reflector, transmits the light received from the latter back through a hole in its center to the eyepiece placed behind it. -- Grego…

A concave cut made in the teeth of some saw blades.

Depressed; concave; gaunt; sunken. With hollow eye and wrinkled brow. Shak.

A curve traced by a point in the circumference of a circle which rolls on the concave side in the fixed circle. Cf. Epicycloid, and Trochoid.

ve, traced by a point in the radius, or radius produced, of a circle which rolls upon the concave side of a fixed circle. See Hypocycloid, Epicycloid, and Trochoid.

f toothed birds found in the American Cretaceous formation. It is remarkable for having biconcave vertebræ, and sharp, conical teeth set in sockets. Its wings were well developed. It is the type of the order Odontotormæ.

An extinct genus of marine reptiles; -- so named from their short, biconcave vertebræ, resembling those of fishes. Several species, varying in length from ten to thirty feet, are known from the Liassic, Oölitic, and Cretaceous formations.