SYNOPSIS OF THE GENERA. xiii 



Limoptera, Hall. Shell Large, inequivalve, inequilateral, sul)(|uadrate, 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. 

 [nter-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 stria?. 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 stria?. Test with concentric stria?. 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 



