978 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
REUSCHELLA EDSONI (Bassler) 
Plate 148, D, figures 27-29 
Dalmanella edsoni BASSLER, Cambrian and Ordovician: Maryland Geol. Surv., p. 243, pl. 49, 
figs. 20, 21 (not 17-19 = Reuschella americana Ulrich and Cooper), 1919.—Kay, Bull. 
Geol. Soc. Amer., vol. 48, p. 302, pl. 10, 1937. 
Large, slightly wider than long, cardinal extremities acute or obtuse depend- 
ing on width of hinge; lateral margins gently rounded; front margin truncated. 
Anterior commissure strongly sulcate. Surface fascicostellate. 
Pedicle valve marked by a prominent subcarinate median fold that increases 
in height to the middle or slightly anterior to the middle, after which it slopes to 
the anterior margin. Slopes flanking fold long and moderately steep. Areas 
bounding fold gently convex. Inside the pedicle valve the muscle field is fairly 
large, in length about equal to one-tenth the length of the valve. Width of muscle 
field about equal to its length. Diductor scars large. 
Brachial valve gently convex in lateral profile, with the greatest convexity at 
about the middle. Sulcus prominent, widening and deepening anteriorly to the 
front margin where it occupies slightly more than a third of the width of the 
valve. Folds bounding sulcus gently convex with gentle slopes to the cardinal 
and lateral margins. Interior unknown. 
Measurements in mm.— 
Hinge 
Length Width width 
Tsectotype «(pedicle -valvee) »\« oj. ais « s::0/<:0,0)0/<es 24.9 20.4 34.0 
Paratype (brachial valve 66169b).......... 21.0 27.9 20.6 ? 
Types.—Lectotype: 66169d; figured paratypes: 66169b,c; unfigured paratype: 
661692, e. 
Horizon and locality—Trenton group (Sherman Fall formation) in Vermont: 
Shipyard Bay, Highgate Springs, St. Albans (15’) Quadrangle. 
Discussion—This species is distinguished by the strong fold continuous from 
beak to anterior margin and the consequent deep and wide sulcus in the brachial 
valve. It differs from R. americana in the greater strength of the fold and sulcus. 
In defining this species Bassler used 7 specimens, 2 of which came from 
Pennsylvania and 5 from Vermont. The lot from Pennsylvania consists of 
3 pieces representing 2 specimens. Figures 17 and 19 of plate 49 in the Mary- 
land volume represent counterparts of the same specimen. It is here recom- 
mended that the Pennsylvania specimens be excluded from the species because 
they have characters different from those of the Vermont specimens and are here 
called R. americana. Inasmuch as Bassler intended to honor George E. Edson 
of St. Albans, Vt., one of the Vermont specimens should be selected as type 
specimen. Specimen 66169d is selected from Bassler’s cotype lot from Highgate 
Springs, Vt. Although this specimen was not figured by Bassler, it is the most 
complete of the lot and shows best the specific characters emphasized herein. 
