380 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
G. aff. G. bellarugosa Butts, Virginia Geol. Surv. Bull. 52, pt. 2, p. 93, pl. 90, figs. 25-32, 
1942. 
Shells of medium to large size for the genus, rectangular in outline; slightly 
wider than long. Hinge narrower than the width at the middle. Cardinal ex- 
tremities obtuse or forming a right angle. Lateral margins straight or sloping 
outward to about the middle. Anterolateral extremities narrowly rounded ; front 
margin straight or slightly emarginate. Greatest width slightly anterior to mid- 
dle. Anterior commissure rectimarginate to slightly sulcate. Valves subequal 
in depth; strongly convex. Surface multicostellate, costellae added by implanta- 
tion and bifurcation in 3 generations. Seven costellae occupy the space of 5 mm. 
at the front of a valve 17 mm. in length, and §8 costellae were counted on the 
same valve. Costellae crossed by imbrications swollen into blunt spines. Imbri- 
cations marked by fine, concentric, elevated threads. 
Pedicle valve unequally convex in lateral view with the greatest convexity lo- 
cated just posterior to the middle. Anterior profile broadly arched. Umbo flat- 
tened ; slopes to the posterolateral margins moderately steep and slightly concave. 
Median region swollen; anterior and anterolateral slopes convex, not very steep. 
Beak only slightly elevated above the posterior margin. Palintrope strongly 
apsacline to procline; interarea slightly curved. 
Brachial valve unequally convex in lateral profile; greatest convexity located 
slightly anterior to the umbo, anterior two-thirds flattened. Anterior profile 
moderately convex, broadly indented medially. Sulcus deepest and narrowest at 
the umbo, widening anteriorly to occupy about one-third the width at the an- 
terior margin. Two primary costellae occupying the sulcus at the umbo, increas- 
ing to 7 or 8 costellae at the front margin. Costellae bounding sulcus often 
stronger and more prominent than the rest. Flanks bounding sulcus moderately 
swollen; slopes to the lateral and posterolateral margins steep, concave. Beak 
strongly incurved, often overhanging pedicle interarea; umbo swollen; umbonal 
region forming deepest part of valve. 
Pedicle interior with elongate diductor impressions extending a short distance 
anterior to the adductor track to the posterior one-third to one-half of the valve. 
Adductor track wide ; adjustor scars small. Median ridge of brachial valve mod- 
erately elevated; brachiophores and cardinal process small. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
UIE C IG. oo wins ob ne dies a e haae's 15.5 15.3 18.7 17.0 10.8 
Paratype (110082c)........ 11.3 11.3 14.3 12.8 6.5 
“s (98200b) ) 20 Fi 13.2 12.6 16.4 14.3 7.5 
fs (110082e)........ 10.3 10.1 13.4 11.3 5.3 
s (110086a)........ 7.8 7.6 9.8 8.8 4.8 
: (GGIOOSG6D)) ce 1c. 5.4 5.6 7.6 7.0 3.3 
4 (EYOOSGE)) 5 oss s,s 3.6 3.5 5.1 4.4 2.0 
a (UIOOSGE ioe cise one 17 1.9 2.4 2.1 1.0 
Types.—Holotype: 98209a ; figured paratypes: 98209d, 110082a-e; unfigured 
paratypes: 98209b,c,e, 110082f-h, 110086a-d. 
