PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 953 
DALMANELLA WINCHELLI Cooper, new name 
Plate 158, D, figures 15, 16 
Orthis (Dalmanella) hamburgensis ? WINCHELL and ScHUCHERT (not Walcott, 1884), Geol. 
Minnesota, vol. 3, pt. 1, p. 440, pl. 33, figs. 14-16, 1895. 
This new name is proposed for Dalmanella hamburgensis Winchell and Schu- 
chert which is totally unlike Orthis hamburgensis Walcott from the Lower 
Ordovician (Goodwin formation) of the Eureka District, Nev. The Nevada 
shell is the type species of the genus Nanorthis, whereas the Minnesota shell has 
the structure of true Dalmanella. 
Figured specimens.—48758a,b. 
Horizon and locality—Decorah formation (Guttenberg member-Rhinidictya 
bed) in Minnesota: At St. Paul. 
Discussion—The National Museum collection contains a few coarsely costel- 
late dalmanellids with wide hinge that may ultimately prove to belong to the 
genus Dalmanella with nearest relationships to D. winchelli. These occur at 
several horizons. 
Family ONNIELLIDAE Opik, 1933 
Dalmanellacea in which the muscle field of the pedicle valve is bilobed, the 
diductor scars not enclosing the adductor impressions. Brachiophores simple 
and bladelike, without fulcral plates in the adult. 
Genus ONNIELLA Bancroft, 1928 
Onniella BANcrort, Mem. Manchester Lit. Phil. Soc., vol. 72, p. 55, 1928; Journ. Paleont., 
vol. 19, No. 3, p. 211, 1945. 
ONNIELLA ? AMERICANA Cooper, new species 
Plate 37, C, figures 8-14 
Shell attaining a width of about 3 inch, wider than long, subrectangular in 
outline ; sides broadly rounded; anterior margin nearly straight. Brachial valve 
convex ; pedicle valve convex at the rear but moderately concave in the median 
region. Surface multicostellate, costellae numbering 2 or 3 to the millimeter at 
the front margin. 
Pedicle valve moderately concave in lateral profile, broadly concave in anterior 
profile. Beak small, umbo subcarinate, the angulation continued anteriorly as 
a low and narrow fold nearly to the front margin. Fold at front margin broad 
and shallow. Flanks bounding fold concave. Posterolateral and lateral extremi- 
ties flattened. Interarea short, apsacline. Pedicle muscle field subquadrate, 
moderately large. 
Brachial valve evenly and gently convex in lateral profile, broadly and gently 
convex in anterior profile but with the middle marked by a narrow depression. 
Umbo sulcate, sulcus extending to anterior margin, narrow in the posterior two- 
thirds but widening anteriorly. Flanks bounding sulcus narrowly rounded; lat- 
eral slopes short, moderately steep. 
