AVICULID. Qt 
GuypropEsMA, Hall, 1883. 
Type, G. erectum, Conr. Hamilton Group; N. Y. 
Ligamental area striated, continuous; hinge 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 rays. 
G. birostratum, Hall. Chemung Group; New York. 
LeropreriA, Hall, 1883 
Distr.—T sp. Fossil. Hamilton Group; N. Y. ZL. 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. JL. potens, Hall. 
SuBFraMILy PH RNIN. 
Cartilage situated in a number of transverse marginal grooves 
of the hinge-line. Anterior muscular scar generally very small. 
Perna, Bruguiére, 1792. 
Etym.— Perna, a shell-fish (resembling a gammon). _(Pliny.) 
Syn.—Melina, Retz,1788. Isognomon, Klein,1753. Pedalion, 
Solander. Hippocheeta, Sangiovanni. 
Distr.—18 sp. Tropical seas; West Indies—India—West 
America. Fossil,30 sp. Trias—; United States, Chili, Europe. 
P. ephippium, Linn. (cxxxi, 64). P. Mulletr, d’Orb. (exxx, 52). 
Shell nearly equivalve, compressed, subquadrate; area wide, 
cartilage-pits numerous, elongated, close-set ; right valve with a 
byssal sinus; muscular impression double. 
The Pernas vary in form like the Avicule ; 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 
byssal 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. 
Rupellensis (=? Pulvinites Adansoni, Defrance, 1826 [exxx, 53]). 
Coral-rag, Rochelle. 
