376 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
margin broadly rounded. Anterior commissure gently sulcate. Surface multi- 
costellate ; costellae subangular and appearing in 3 generations by implantation. 
A specimen about 12 mm. in length has about 40 costellae which are crossed by 
closely spaced imbricated lamellae. 
Pedicle valve strongly convex in lateral profile with the greatest convexity be- 
tween the umbo and the middle of the valve. Anterior profile strongly convex. 
All slopes from swollen preumbonal region steep. Interarea curved, elongate, 
apsacline. Beak pointed forming an angle of 110°. Delthyrium narrow. 
Brachial valve unequally convex in lateral profile, the umbonal region having 
the greater convexity. Moderately convex anterior to the umbonal region. An- 
terior profile less convex than that of the pedicle valve and medially sulcate. 
Sulcus deep at the umbo, widening anteriorly and in old shells becoming much 
shallower and nearly obsolete at the front margin. Sulcus occupying 5 mm. of 
the front margin of a specimen 12.5 mm. wide. Two costellae occupying the 
sulcus at the beak, increasing to 8 at the front margin of an adult. Flanks bound- 
ing sulcus moderately convex; slopes to the cardinal extremities steep and con- 
cave. Beak much incurved; interarea short. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype. 33.2% chai 10.5 9.0 10.8 9.3 6.8 
Paratype (110076a).. 12.2 10.8 12.7 9.5 9.0 
ss (110076b).. 12.0 10.6 12.8 10.0 7.0 
Types.—Holotype: 110075a; figured paratypes: 110074, 110075b; unfigured 
paratypes: I10075c; 110076a-e. 
Horizon and locality.—Crown Point formation (bed B, division 3 of Brainerd 
and Seely) in New York: At Chazy and vicinity, Rouses Point (15’) Quad- 
rangle; Valcour Island and quarry 4 mile north of the Normal School, Platts- 
burg, Plattsburg (15’) Quadrangle. 
Discussion.—This species is characterized by its strongly convex valves, swol- 
len umbonal regions and prominent sulcus on the brachial valve. The species has 
some features that remind one strongly of G. concinnula but has a much larger 
shell and much more convex valves. Resemblance to G. bellarugosa, with which 
it has long been confused, is remote. Although the size of G. sulcata and of the 
type specimens of G. bellarugosa are about the same, the Chazyan shell is more 
convex in both valves and has deeper sulcus on the brachial valve and a more 
incurved beak on the pedicle valve. 
GLYPTORTHIS TRANSVERSA Cooper, new species 
Plate 50, F, figures 24-28 
Shell small for the genus, width about 14 times the length; outline subellipti- 
cal; hinge narrower than the width at the middle; sides somewhat narrowly 
rounded; anterior margin gently rounded; valve subequally convex; anterior 
commissure rectimarginate. Surface marked by about 26 narrowly rounded 
