260 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
flattened on the posterior side in lateral profile; pseudointerarea broad; inter- 
trough fairly wide and deep, extending to the beak; foramen small, located on 
the posterior side of the beak at the place of origin of the intertrough, and having 
a narrow, shallow groove anterior to it. 
Brachial valve roundly elliptical in outline; flat to moderately concave in 
lateral profile. 
Pedicle interior with strong ridge on palintrope representing internal track 
of intertrough; foramen surrounded by a thickened and elevated rim; brachial 
interior with prominent median septum originating at the middle of the valve in 
young specimens but never growing much farther posteriorly in the adult ; median 
septum highest near the front margin, notothyrial region closed by a short but 
prominent shelf. 
Genotype.—Scaphelasma septatum Cooper, new species. 
Discussion.—This genus is characterized by its fairly symmetrical conical form, 
deep intertrough with foramen set in its anterior end and the median septum oc- 
cupying the anterior half of the valve. In the latter respect it resembles Rhyso- 
treta, but the septum never grows to the rear of the shell as in the latter genus. 
It also resembles Rhysotreta in having the small shelf that grows anterior to 
the beak of the brachial valve and overhangs the cavity between the median sep- 
tum and posterior margin. Scaphelasma is quite unlike Rhysotreta in the size 
of the foramen and the ornamentation. 
SCAPHELASMA SEPTATUM Cooper, new species 
Plate 18, J, figures 65-73 
Shell small, generally straw-yellow in color, transversely elliptical in outline 
and conical in profile. Surface in the umbonal region marked by fine concentric 
lines ; but in the marginal region by strong undulations or imbrications. 
Pedicle valve forming a symmetrical cone with convex sides in anterior profile ; 
lateral profile conical with the beak slightly posterior to the center, the anterior 
slope being flat to slightly convex and longer than the posterior slope ; posterior 
slope steep and convex; intertrough wide, extending to foramen. Foramen lo- 
cated somewhat posterior to the beak at the end of a narrow and shallow trough. 
Interior as described for the genus. 
Brachial valve with posterior half marked by fine growth lines only but an- 
terior half imbricate with strong plaits. Lateral profile convex in the umbonal 
region, becoming concave anterior to the umbo but convex again in the plaited 
portion ; anterior profile nearly flat except for the median region which is gently 
concave ; beak narrowly swollen and protruding posterior to the posterior mar- 
gin; swollen umbonal areas extend anterolaterally to the plaited area; sulcus 
originating just anterior to umbo and extending to anterior margin. 
Measurements in mm.— 
Length Width Thickness 
Holotype (pedicle valve) 00.0050... cece cones 1.1 1.4 0.6 
Paratype (brachial valve 116819h) ........... Te 1.4 0.3 
