820 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. | 127 
Superfamily StRoPHOMENACEA Schuchert, 1896 
Usually with thin visceral cavity; pseudodeltidium present; foramen apical 
when present; cardinal process double shafted ; chilidium present. 
Family LEPTAENIDAE Cooper, new family 
Compressed to faintly lenticular Strophomenacea with large apical foramen. 
Genus LEPTAENA Dalman, 1828 
Leptaena DaLMAN, K. Svenska Vet.-Akad. Handl. for 1827, pp. 93, 94, 1828. 
LEPTAENA ORDOVICICA Cooper, new species 
Plate 208, B, figures 19-21; plate 212, C, figure 32; plate 228, B, figures 8-18 
Leptaena tenuistriata Sowerby var. BAssLerR, Cambrian and Ordovician: Maryland Geol. 
Surv., p. 260, pl. 40, fig. 2, 1919. 
Shell of about medium size for the genus, hinge forming the greatest width, 
the cardinal extremities angular and alate. Length equal to about three-fourths 
the width at the middle. Lateral margins excavate just anterior to the cardinal 
extremities, narrowly rounded at the anterolateral extremities and broadly 
rounded at the front margin. Surface unequally costellate, 1 to 2 of the smaller 
costellae alternating with the stronger ones. At the front margin 18 costellae 
occupy a space of 5 mm. Body with thin concentric undulations. 
Pedicle valve with visceral region or body depressed below (brachiad) the rim 
marking place of geniculation; umbonal region swollen, the swelling continued 
anteriorly as a low fold nearly to the rim of geniculation. Areas surrounding 
swollen fold and in front of it concave with gentle slopes from the umbo. Genicu- 
lated rim strong, located 12 mm. anterior to the beak, narrowly rounded in sec- 
tion, sharply bent at the anterolateral extremities of the body and extending 
with a broad curve convex outward to the anterior side of the ear. Angle of 
geniculation about 90°. Geniculated part nearly flat in profile, descending steeply 
to the anterior margin but less steeply around the sides to the ears. Interarea 
short, delthyrium wide, partially covered by a short pseudodeltidium. 
Brachial valve closely fitting the pedicle valve; umbo concave with concavity 
extended nearly to middle ; between concave area and point of geniculation valve 
is gently convex; geniculated area marked by a deep groove. Interarea short. 
Interior of pedicle valve with subcircular to subflabellate muscle field ; diductor 
scars large, semiflabellate ; teeth strong, dental plates thick and flaring; pedicle 
callist small, apical. Entire visceral region tuberculate. Interior of brachial valve 
with short, low, median ridge, somewhat thickened adductor field and tubercu- 
late surface. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
THOIOEY De pana ates a ae 11.0 ? 20.3 23.0 ? 
Paratype (117666).... 15.4 a of 19.6 20.3 ? 
(117664a)... 10.4 ? 16.4 13.6 ? 
a (CUN7 O07.) ere ony ve 13.1 20.5 24.0 ke 
