874 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
remainder is gently convex. The surface is marked by fairly strong costellae, 
about 15 in 5 mm. at the anterior margin. Fine costellae alternate with several 
of the stronger ones. 
Measurements in mm.—117699a, length 23.9, brachial length 22.5, midwidth 
(based on half-width) 27.4, thickness 4.9. 
Figured specimens.—117698, 117699a. 
Horizon and locality—Arline formation in Tennessee: About 100 feet below 
the top in the glade 4 mile southeast of Friendsville, Concord (T.V.A. 138-SW) 
Quadrangle. 
Discussion—The specimens are not like any described species. 
Genus TRIGRAMMARIA Wilson, 1945 
Trigrammaria Wixson, Trans. Roy. Soc. Canada, ser. 3, vol. 39, sec. 4, p. 140, 1945; Geol. 
Surv. Canada, Bull. 8, p. 108, 1946. 
The description by Dr. Wilson is as follows: “The species and its varieties, 
like Strophomena have a resupinate pedicle valve, concave anteriorly, and a 
convex brachial valve. They are triangular in outline; the brachial valve being 
more or less sharply geniculate with a broad anterior fold prolonged beyond the 
general contour, and a corresponding sinus in the pedicle valve; a small pedicle 
muscle scar and three septa in the brachial valve ; the median septum is prolonged 
and two lateral ones added, both curving inward towards the median septum; 
pseudopunctae forming a fine irregular network. 
“The genotype of Strophomena, S. rugosa cannot now be examined. The 
first Strophomena described and illustrated from North America was Producta 
incurvata Shepard, 1838, now recognized as S. filitexta Hall. This species illus- 
trates the typical form, the deeply sculptured pedicle muscle scar and a single 
strong median septum, and the radial arrangement of the punctae, and it is here 
regarded as typical of the genus Strophomena. 
“Several score of S. filitexta were examined, none of them complete, but all 
showed one stout median septum or its impression. Trigrammaria differs, then, 
from Strophomena in having three septa in the brachial valve, in its small pedicle 
muscle scar, and in the irregular network arrangement of the [pseudo] punctae. 
It differs from the following genus Microtrypa in being triangular in outline and 
in being convex and more or less geniculate. In addition, the median septum of 
Microtrypa divides anteriorly making 4 septa in all. 
“The name is derived from tria (three) and gramme (a line) and refers to 
the three fine septa.” 
Strophomena winchelli Hall and Clarke is referred to this genus because of 
the brachial folding and triseptate interior of the brachial valve. 
TRIGRAMMARIA TRIGONALIS PRIMA Wilson 
Trigrammaria trigonalis prima Witson, Trans. Roy. Soc. Canada, ser. 3, vol. 39, sec. 4, 
p. 143, pl. 2, figs. 3, 4, 1945; Geol. Surv. Canada, Bull. 8, p. 110, pl. 10, fig. 20, 1946. 
Type.—Holotype: G.S.C. 7658. 
Horizon and locality—Chaumont formation in Quebec; La petite Chaudieére, 
west of Hull. 
