424 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
cavities ; muscle area somewhat quadrate, gently indented anteriorly and extend- 
ing about one-third the length; pallial impressions not strongly marked. 
Brachial valve gently convex in lateral profile; broadly convex in anterior 
profile and: with the median region more or less strongly indented. Umbo sul- 
cate ; sulcus narrow and shallow to moderately deep in the posterior half, widen- 
ing and shallowing, often to disappearance anteriorly; flanks bounding sulcus 
somewhat narrowly rounded and with short but fairly steep lateral and postero- 
lateral slopes. Interior with short, low median ridge, short brachiophores, and 
stout but short cardinal process; lateral processes occasionally developed. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
FIGIOLY Pe: fae 2 oetcaatea’s sees tas 21.7 21.5 26.0 22.0? 8.5 
Paratype: (1104258) oy: tO. 25.5 24.8 31.2.7 ? 9.8 
H (CBTO4Z5e) a saad ines 21.7 21.5 27.3? 23.4? 8.2 
( TROAB SID a ais eiaicreain 21.1 20.8 28.7? 27.2 8.1 
ff (11a4257)) [.1. .. goer 18.6 18.3 23.3 20.8 7.0 
Types.—Holotype: 110414b,c (these are etched valves of one individual) ; 
figured paratypes: 110414a, 110425b,e; unfigured paratypes: 110425a,c,d,f-i, 
measured paratype 110425}. 
Horizon and locality—Lincolnshire formation in Tennessee: 4 mile north of 
Eidson, Kyles Ford (T.V.A. 170-SE) Quadrangle. 
Discussion —This species is represented by numerous specimens, but not one 
of them is perfect enough to permit the making of really good measurements. 
The species is characterized by its large size, generally strong fold and fairly 
deep and wide sulcus, although both features are variable. It differs from 
M. quadrata in the stronger fold and sulcus. 
MULTICOSTELLA QUADRATA Cooper, new species 
Plate 63, C, figures 13-21 
Shell large for the genus, slightly wider than long; hinge forming the widest 
part; sides nearly straight ; anterolateral extremities rounded; anterior margin 
truncated to gently rounded; cardinal extremities slightly auriculate; anterior 
commissure rectimarginate ; lateral commissure very slightly deflected in the di- 
rection of the brachial valve in the posterolateral region ; surface multicostellate, 
costellae rounded and swollen, closely crowded with striae narrower than the 
costellae ; costellae numbering 12 in 5 mm. at the anterior margin. 
Pedicle valve unevenly convex with the most convex part in the posterior half 
and with the anterior half flattened; anterior profile forming a broad triangle 
with the median region narrowly rounded and the flanks sloping by a low descent 
to the margins; umbo narrowly plicate to subcarinate, the carina continued to 
the middle as a well-defined fold but becoming indistinct or obsolete anterior 
to the middle; flanks slightly swollen and descending by a very gentle slope to 
the margins ; posterolateral area small, flattened ; interarea moderately long, mod- 
erately apsacline. Interior with small teeth; dental plates obsolete; muscle area 
