764 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Family BIMURIIDAE Cooper, new family 
Concavo-convex, smooth or lamellose Plectambonitacea with apical foramen 
in pedicle valve ; simple cardinal process and 2 or 3 long divergent median septa 
in the brachial valve. 
Genus BIMURIA Ulrich and Cooper, 1942 
Bimuria UtricH and Cooper, Journ. Paleont., vol. 16, No. 5, p. 622, 1942. 
Shell moderately large reaching a width of about an inch, semicircular to semi- 
elliptical in outline, concavo-convex in profile. Pedicle interarea curved, longer 
than the brachial one, anacline; brachial interarea hypercline. Delthyrium in 
well-preserved individuals partially closed by a short and rudimentary pseudo- 
deltidium. Beak perforated by a tiny foramen. Umbonal region generally 
smooth ; more or less of remaining surface covered by thin, wrinkled shell lamel- 
lae. Shell structure pseudopunctate. 
Pedicle interior with small, rudimentary teeth; dental plates obsolete ; diductor 
and adjustor scars located at the base and sides of the delthyrial cavity ; diductor 
scars large ; adductor scars indistinct. Vascula media strong, extending to about 
the middle of an adult shell, then branching, the inner branches extending nearly 
to the margin, while the outer ones arch slightly and extend nearly to the margin 
where they again branch. 
Brachial valve with elongate, slender, widely divergent brachial processes. 
Chilidial plates strongly developed, attached to brachial processes and sides of 
notothyrium by callus. Cardinal process simple, myophore slender or some- 
what expanded, shaft short, united with a thin median septum that extends for 
nearly the full length of the valve and is located between 2 slightly divergent 
lateral septa. Lateral septa high and thin in the young, overgrown and nearly 
obliterated in old shells by callus deposit on their inner and outer sides. Adduc- 
tor impressions somewhat flabellate, located on the posterior portion of the callus 
deposits on the outside of the lateral septa. 
Genotype—Bimuria superba Ulrich and Cooper, Journ. Paleont., vol. 16, 
No. 5, p. 623, pl. go, figs. 13-18, 1942. 
Discussion.—Species of this genus have been assigned to Plectambonites= 
Sowerbyella and Christiania. From the former it differs by its exterior and the 
presence of the longitudinal lamellae inside the brachial valve. No taxonomic 
relationship exists between Bimuria and Sowerbyella. Bimuria resembles Chris- 
tiania in external form but is never so elongated as the species of that genus and 
is usually lamellose whereas Christiania is smooth. The brachial interior of 
Bimuria differs from that of Christiania in the possession of a simple cardinal 
process rather than a rafinesquinoid, bilobed process such as is present in 
Christiania. 
Outside the United States in the Stinchar limestone of the Girvan District, 
Scotland, Plectambonites ? youngiana (Davidson) is referable to Bimuria. 
