Lamellibrastchiata. 406c 



Pty diopter ia, Hall. Differs from Actinopteria in the nasute ante- 

 rior extremity, and large straight wing marked by a strong longitudi- 

 nal fold. Hinge-line narrow, linear ; furnished with one or two linear 

 oblique cardinal and lateral teeth. Surface with fine rays. 



Examples — Ptychopteria Beecheri. PI. hi, figs. 15, 16. 



Ptychopteria Salamanca. PI. iii, figs. 17, 18. 

 Ptychopteria Proto. PI. iii, fig. 19. 



Limoptera, Hall. Shell large, inequivalve, inequilateral, subquad- 

 rate, strongly alate on the posterior sifie, 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 — Limoptera macroptera. PI. iii, figs. 5, 6. 

 Limoptera cancellata. PI. iii, fig. 7. 



Glyptodesma, Hall. Shell aviculoid, erect or moderately oblique ; 

 inequivalve. Ligament external. Ligamental area striated, continu- 

 ous. Hinge with two strong lateral teeth, and numerous irregular 

 transverse plications along the cardinal margin. In form the shells of 

 this genus resemble Actinodesma ; but they have not the prominent 

 diverging teeth of tha»t genus. Surface marked by concentric striae. 



Example — Glyptodesma erectum. PL iv, figs. 1-8. 



'a 1 - 



Leiopteria, Hall Shell aviculoid, oblique, subrhomboidal. Anterior 

 extremity 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 clavicle. 



Examples — Leiopteria Rqfinesquii. PI. iv, figs. 9, 10. 

 Leiopteria JDekayi. -PI. iv, fig. 11. 



Leptodesma, Hall. In its prevailing forms this genus is similar to 

 Leiopteria, except that the anterior end is always nasute and acute in- 

 stead of auriculate and rounded. Hinge narrow^ furnished with a slen- 

 der lateral tooth just posterior to the beak and nearly parallel to the 

 hinge-line. Ligament external. Ligamental area narrow, extending 

 the entire length of the hinge, marked by fine, sharp, longitudinal 

 striae. Test with concentric striae. 



Examples — Leptodesma longispinum. PI. iv, fig. 12. 

 Leptodesma Hector. PI. iv, figs. 13, 14. 

 Leptodesma Jtaecidum. PI. iv, fig. 15. 

 Leptodesma propinquum. PI. iv, fig. 16. 



