AVICULTD^. 211 



Glyptodesma, Hall, 1883. 



Type, G. erectum, Conr. Hamilton Group ; N. Y. 



Ligamental area striated, continuous; binge with two strong 

 lateral teeth, and numerous irregular transverse plications 

 along the cardinal margin. In form like Actinodesma, but 

 without the prominent diverging teeth of that group. 



ECTENODESMA, Hall, 1883. Resembles Glyptodesma in outline, 

 except that the anterior wing is more produced, and both wings 

 more acute at their extremities ; surface ornamented with ra^^s. 

 G. birostratum, Hall. Chemung Group; New York. 



Leiopteria, Hall, 1883. 



Distr. — T sp. Fossil. Hamilton Group ; N. Y. L. Dekayi, 

 Hall. 



Aviculoid, resembling Actinoptera in form ; anterior extremity 

 auriculate ; wing large, extremity produced ; surface without 

 prominent rays. 



LEPTODESMA, Hall, 1883. In its prevailing forms like Leiop- 

 teria, except that the anterior end is nasute and acute, instead 

 of auriculate and rounded ; hinge-line narrow. 12 sp. Chemung 

 Group ; New York. L. potens, Hall. 



Subfamily PERNIN^. ■ 



Cartilage situated in a number of transverse marginal grooves 

 of the hinge-line. Anterior muscular scar generally very small. 



Perna, Bruguiere, 1792. 



Etym. — Perna, a shell-fish (resembling a gammon). (Pliny.) 



Syn. — Melina,Retz,1788. Isognomon, Klein, 1753. Pedalion, 

 Solander. Hippochaeta, Sangiovanni. 



Dutr. — 18 sp. Tropical seas; West Indies — India — West 

 America. Fossil, 30 sp. Trias — ; United States, Chili, Europe. 

 P. ephippium, Linn, (cxxxi, 64). P. Mulleti, d'Orb. (cxxx, 52). 



Shell nearly equivalve, compressed, svibquadrate ; area wide, 

 cartilage-pits numerous, elongated, close-set; right valve with a 

 byssal sinus ; muscular impression double. 



The Pernas vary in form like the Aviculse ; some are very 

 oblique, some very inequivalve, and many fossil species have 

 the posterior side produced and wing-like. In some Tertiary 

 Pernas the pearly layer is an inch thick. 



PULVINITES, Defrance, 1824. (Hypotrema, d'Orb., 1853.) Shell 

 oblong, inequivalve ; right valve flat or concave, with a round 

 bj'Ssal foramen near the hinge ; left valve convex, with a mus- 

 cular impression near the umbo ; hinge-margin broad, curved, 

 with about twelve close-set transverse cartilage-grooves. P. 

 Bupellensis (= 1 Pulviniies Adansoni, Defrance, 1826 [cxxx, 53]). 

 Coral-rag, Rochelle. 



