SYNOPSIS OF THE GENERA. 
xiii 
Limoptera, Hall. Shell large, inequivalve, inequilateral, subquadrate, strongly 
alate on the posterior side, auriculate on the anterior end. Ligamental area 
large, common to both valves, wider in the left valve, longitudinally striate and 
extending to the cardinal extremities. The hinge has an oblique posterior 
tooth and several cardinal folds under the beak. Anterior muscular impression 
very small and deep, situated at the apex of the rostral cavity; posterior 
impression large. Pallial line simple, formed of a series of small deep pits. 
Inter-pallial area with numerous small pits for the attachment of umbonal 
muscles. Test radiated; radii becoming obsolete with age. Examples, pi. xcii, 
figs. 3, 8, 9. 
Glyptodesma, Hall. Shell aviculoid, erect or moderately oblique; inequivalve. 
Ligament external. Ligamental area striated, continuous. Hinge with two 
strong lateral teeth, and numerous irregular transverse plications along the 
cardinal margin. In form the shells of this genus resembles Actinodesma; 
but it has not the permanent diverging teeth of that genus. Surface marked 
by concentric striae. Examples, pi. xi, figs. 3, 4; pi. xiii, figs. 5, 10; pi. 
lxxxvi, figs. 3, 8. 
Leiopteria, Hall. Shell aviculoid, oblique, sub-rhomboidal. Anterior extrem¬ 
ity auriculate; wing large, extremity produced. Test without proper rays. 
Ligament external. Ligamental area marked by fine parallel longitudinal 
striae. Hinge with one or two oblique slender lateral teeth. The cavity of 
the beak is partially separated from the anterior end by a short partition or 
diaphragm. Examples, pi. xx, fig. 17; pi. lxxxviii, figs. 5, 27. 
Leptodesma , Hall. In its prevailing forms it is. similar to Leiopteria, except 
that the anterior end is always nasute and acute instead of auriculate and 
rounded. Hinge narrow, furnished with a slender lateral tooth just posterior 
to the beak and nearly parallel to the hinge-line. Ligament external. Liga¬ 
mental area narrow, extending the entire length of the hinge, marked by fine, 
sharp, longitudinal striae. Test with concentric striae. Examples, pi. xxi, fig. 
14; pi. xxii, fig. 21; pi. xc, fig. 28 ; pi. xci, figs. 9, 16. 
Pteronites, McCoy. This genus is restricted to those possessing the characters 
of the original types. Body very oblique. Hinge-line longer than the body 
