SYNOPSIS OF THE GENERA. 
xii 
Pernopeden * Winchell. Shell like Pecten. Hinge with a central cartilage pit 
and a crenulated hinge-plate on each side below the hinge-margin. This and 
the following genus appear to be more nearly related to the genus Pecten than 
to Aviculopecten. 
Crenipeden, Hall. Like Aviculopecten in form. Hinge furnished with a series 
of small cartilage pits throughout its entire length. Examples, pi. ix, figs. 12,15. 
Aviculopecten, McCoy, is emended to include those forms which have the hinge¬ 
line usually shorter than the transverse diameter, and both ears well-defined. 
Test ornamented with rays. Example, pi. i, fig. 10. 
Lyriopeden, Hall. Differs from the preceding in the short hinge-line and 
very small anterior ear. Test usually ornamented with strong rays. Example, 
pi. viii, fig. 8. 
Pterinopeden, Hall. Hinge-line long. Ears not well-defined, being simple 
expansions or extensions of the upper lateral margins to the hinge-line. Test 
ornamented with rays. Examples, pi. ii, fig. 18; pi. v, fig. 6. 
Pterinea, Goldfuss. Shell inequivalve, inequilateral; posterior side alate; 
anterior end nasute or auriculate. Ligament internal; ligamental area longi¬ 
tudinally striated. Cardinal teeth two or more. Lateral teeth linear oblique. 
Posterior muscular impression large, situated on the post-umbonal slope. 
Anterior muscular impression small, situated within the rostral cavity. Test 
ornamented with rays. Examples, pi. xv, figs. 1-21; pi. lxxxiii, fig. 12. 
S. g. Vertumnia, Hall. Differs from Pterinea in having the right valve convex, 
and the left flat or concave. Hinge area narrow. Example, pi. xxiv, fig. 12. 
Adinopteria, Hall. Characterized from Pterinea in the absence of a broad 
striated ligamental area and strong cardinal and lateral teeth. Right valve 
sub-convex. Surface with fine rays. Examples, pi. xvii, fig. 26 ; pi. xviii, fig. 
13; pi. xix, fig. 3. 
Ptychopteria, Hall. Differs from Actinopteria in the nasute anterior extrem¬ 
ity, and large straight wing marked by a strong longitudinal fold. Hinge¬ 
line narrow, linear; furnished with one or two linear oblique cardinal and lateral 
teeth. Surface with fine rays. Example, pi. xxiii, fig. 17. 
See note, page 81. 
