PART, 1 CHAZYAN AND RELATED BRACHIOPODS—-COOPER 377 
costellae with interspaces about equal to the width of the costellae ; imbrications 
3 or 4 to the millimeter. 
Pedicle valve with lateral profile gently convex; anterior profile very broadly 
and moderately convex ; umbonal and median regions moderately convex; pos- 
terolateral slopes moderately steep; interarea curved, strongly apsacline. 
Brachial valve moderately convex in lateral profile and very broadly convex 
in anterior profile; umbo sulcate, sulcus shallow; scarcely attaining the anterior 
margin; flanks bounding sulcus moderately swollen, the swelling extending to 
the posterolateral areas which are not depressed. 
Measurements in mm.—Holotype, length 5.8, brachial length 5.2, width 7.8, 
hinge width 6.6, thickness 3.3. 
Type—Holotype: 116939. 
Horizon and locality.—St. Martin formation in Quebec, Canada: At Belanger, 
2 miles south of Cap St. Martin. 
Discussion.—This little species is not like any of the other Chazy species of 
Glyptorthis, most of which have the unequal costellae, subquadrate outline, and 
wide sulcus of G. concinnula and G. sulcata. Its transverse form and subequal 
costellae suggest some of the stratigraphically higher species, but it is not sub- 
carinate like the small Benbolt or Hogskin forms. 
GLYPTORTHIS UNCINATA Cooper, new species 
Plate 43, B, figures 4-7; plate 46, B, figures 5-10; plate 50, E, figures 19-23 
Shell small for the genus, wider than long with the length about two-thirds the 
width; hinge forming the widest part or narrower than the width at the middle 
in adults ; sides nearly straight, slightly oblique or gently rounded ; anterior mar- 
gin gently rounded; anterior commissure gently and broadly sulcate; surface 
ornamented by 22 to 24 subangular costae crossed by strong imbrications about 
2 to the millimeter ; imbrications often produced over the costella into a hollow 
spine. 
Pedicle valve gently convex in lateral profile; somewhat broadly convex in 
anterior profile with the median region narrowly rounded and the sides slop- 
ing steeply; median region narrowly swollen from umbo to anterior margin to 
produce a poorly defined fold. Interarea long; nearly catacline. 
Brachial valve very gently convex in lateral and anterior profiles; umbo sul- 
cate ; sulcus deepening and widening anteriorly to occupy about half the width 
at the front margin; sulcus occupied by 4 to 6 costellae. 
Pedicle interior with small teeth ; poorly developed lateral plates ; short, widely 
divergent, receding dental plates; deep delthyrial cavity but lightly impressed 
short muscle field. Brachial interior with thickened cardinal process, short 
brachiophores, low median ridge, and not greatly thickened notothyrial platform. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hicidtype™ ety. cc eee es 6.1 6.0 8.7 8.6 3.9 
Paratype (116942) .... 5.5 5.0 7.5 7.8 312 
