822 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
HESPERINIA Cooper, new genus 
(Greek hespera, west) 
Small, subrectangular shells with the hinge equal to or wider than the mid- 
width; plano- to slightly concavo-convex; surface multicostellate. Foramen not 
seen. Shell substance coarsely pseudopunctate. 
Pedicle valve with long interarea, wide delthyrium covered by a pseudodel- 
tidium. Teeth large; dental plates oblique, moderately long. Musculature not 
known. 
Brachial interior with moderately strong and erect cardinal process consisting 
of 2 lobes and suggesting that of Leptaena. Brachiophores, flat blades, obliquely 
situated on each side of the cardinal process and supported by shell substance 
as in the Strophomenidae ; adductor field large ; subperipheral rim well developed 
and channeled by pallial trunks. 
Genotype-—Hesperima kirki Cooper, new species. 
Discussion.—The external appearance of this little genus is very close to that 
of Pomatotrema of the high Canadian Period. The interior details, however, are 
totally unlike in the two genera because Pomatotrema has a simple cardinal 
process whereas Hesperinia has a bilobed or leptaenoid cardinal process. Indeed, 
this species suggests an early leptaenoid. 
Affinities with Leptaena occur also in the configuration of the valves, the 
pseudodeltidium, the subperipheral rim and cardinal process of the brachial valve 
interior. The shells differ from Leptaena or Dactylogonia in interior details of 
the brachial valves, Hesperimia lacking the adductor ridges, the thickened noto- 
thyrial platform, and thick but short median ridge. These features also dis- 
tinguish this genus from Goniotrema which is also a Pogonip genus. 
HESPERINIA KIRKI Cooper, new species 
Plate 213, E, figure 25; plate 2209, C, figures 9-15 
Shells small, attaining a width of about 4 inch; subrectangular in outline; 
sides gently rounded; anterior margin broadly rounded; cardinal extremities 
nearly a right angle; hinge equal to the midwidth. Surface finely costellate, cos- 
tellae numbering about 5 to the millimeter at the anterior margin. 
Pedicle valve gently convex in lateral profile and with the maximum convexity 
in the posterior two-thirds; anterior third somewhat abruptly bent toward the 
brachial valve. Anterior profile broadly and fairly strongly convex. Umbonal 
and median regions swollen; lateral slopes long and only moderately steep; an- 
terior slope shorter and steeper than the lateral slopes. Interarea moderately 
long, apsacline ; pseudodeltidium short, convex. 
Brachial valve nearly flat in lateral and anterior profile; anterior margin 
gently curved in the direction of the brachial valve. Interior with narrow margi- 
nal thickening. 
