976 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Family HETERORTHIDAE Schuchert and Cooper, 1931 
Subfamily HARKNESSELLINAE Bancroft, 1928 
Biconvex, fascicostellate Heterorthidae having a prominent fold on the pedicle 
valve and a corresponding sulcus on the brachial valve. 
Genus REUSCHELLA Bancroft, 1928 
Reuschella BANcRort, Mem. Manchester Lit. Phil. Soc., vol. 72, p. 180, 1928—SCHUCHERT 
and Cooper, Mem. Peabody Mus. Nat. Hist., vol. 4, pt. I, p. 139, 1932. 
This genus embraces large shells externally fascicostellate and with endopune- 
tate shell structure. The pedicle valve generally bears a prominent median fold 
and the brachial valve is strongly sulcate. The valves are subequally convex. 
Inside the pedicle valve the muscle field is small with the adductor field occupying 
a shallow depression and the diductor tracks located on each side of it. The den- 
tal plates are generally short but stout. Inside the brachial valve the brachio- 
phores are short and stout and are supported by swelling of shell substance 
along their inner surfaces. The cardinal process has a short shaft borne on the 
swelling that clogs the notothyrial cavity; the myophore is small and trilobate. 
The median ridge is short and low. 
This genus is fairly common in the Middle Ordovician of England and Wales 
but has hitherto not been reported on this continent. It proves now to be com- 
mon in the Oranda formation in Virginia and is known from the Trenton (Sher- 
man Fall) in Vermont. A species has been identified in the Jacksonburg forma- 
tion of New Jersey, and another is known from dark shales under the Eureka 
quartzite in Nevada. 
REUSCHELLA AMERICANA Cooper, new species 
Plate 147, A, figures 1-7; plate 147, B, figures 8-20 
Dalmanella edsoni BASSLER (part), Cambrian and Ordovician: Maryland Geol. Surv., p. 243, 
pl. 49, figs. 17-19 (not 20 and 21), 1919.—Coorer and Cooper, Bull. Geol. Soc. Amer., 
vol. 57, pl. 3, figs. 33, 34, 1946. 
Shell large, rectangular in outline with the width slightly greater than the 
length. Cardinal extremities varying from acute to obtuse; lateral margins 
slightly concave to gently rounded ; anterolateral extremities somewhat narrowly 
rounded; anterior margin truncated. Anterior commissure rectimarginate to 
sulcate. Surface fascicostellate with 5 or 6 well-defined fascicles on each side of 
the fold. Fold consisting of 3 fascicles, a median one and one on each side of it. 
Costellae appearing in 4 generations by bifurcation and intercalation; 7 to 10 
costellae may be counted in 5 mm. at the front margin. 
Pedicle valve gently convex in lateral profile with the greatest convexity in 
the posterior half. Fold originating at the beak where it is very narrowly rounded 
and generally smooth, widening gradually anteriorly and heightening to about 
the middle from which it gradually declines in height to the front margin. Fold 
scarcely distinguishable at the front margin of some specimens except for the 
