212 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve with minute beak and broad apical angle; interior with narrow 
propareas marked by concentric lines and appearing as narrow folds on the pos- 
terior margin. Muscle marks so lightly impressed as to make it impossible to 
determine the individual muscles. Pedicle groove poorly defined. 
Brachial valve generally somewhat deeper than the pedicle valve and usu- 
ally marked medially by a shallow sulcus. Umbo swollen; interior with some- 
what thickened margin, incurved and with a posteriorly directed wave at the 
beak which forms a notch. Muscle scars not deeply enough impressed to 
distinguish. 
Genotype—Acanthambonia minutissima Cooper, new species. 
Discussion.—This genus is suggestive of Leptobolus but differs in the nature 
of the posterior margins of both valves and the ornamentation. The spiny ex- 
terior of Acanthambonia is a means of ready distinction between the two genera. 
The apical structures of both valves are suggestive of Lingulella, but the exterior 
is quite different. The genus is assigned to the Lingulellidae because the apical 
structures are suggestive of that family. The general habit of Acanthambomia is 
so different from that of the other Lingulellidae that the new subfamily is erected 
for it. 
ACANTHAMBONIA MINUTISSIMA Cooper, new species 
Plate 18, D, figures 23-27 
Shell minute, biconvex, the brachial valve having a slightly greater convexity 
than the pedicle valve; beaks inconspicuous; outline nearly circular; surface, 
including posterior margin, marked by fine hairlike spines, and faint concentric 
lines of growth. 
Pedicle valve moderately convex and with the greatest convexity located in 
the posterior third; anterior slope gently convex and moderately steep. Anterior 
profile fairly evenly and broadly convex ; beak small, protruding slightly posterior 
to the posterior margin; umbo and median region inflated. 
Brachial valve fairly strongly convex with the greatest convexity in the pos- 
terior third ; anterior slope moderately long and gently convex, moderately steep ; 
anterior profile swollen in the middle and with short and steep lateral slopes. 
Median sulcus shallow, originating just anterior to the umbo and widening to 
the front margin where it occupies about one-third the width. 
Measurements in mm.— 
Holotype "(pedidles yalvepioO.4 sr kiea4 be RRR tee 1.4 ng 
Paratype. (brachial. yalve_ 1167954) #..jss20< sci eosjensis ations 1.6 1.4 
Types.—Holotype: 116795b; figured paratypes: 116795a,c. 
Horizon and locality—Pratt Ferry formation in Alabama: 0.2 mile south- 
east of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion.—This species differs from A. virginiensis Cooper, new species, 
which occurs at about the same level in Virginia, by its small size and more 
scattered spines. 
