PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER Zig 
which is small and elongate. Diductor-adjustor scars subequal, elongate, nar- 
row, extended anterior to delthyrial cavity ; adductor field confined to delthyrial 
cavity. 
Cardinalia most suggestive of Sowerbyites with long, slender brachial proc- 
esses supported in part by callus deposited under the cardinal process and their 
inner surfaces. Cardinal process tripartite, with a median elevated ridge and two 
lesser ridges on each side of it and separated by deep grooves. Face of cardinal 
process toward the pedicle valve somewhat bulbous. Median septum thin, most 
elevated at its anterior part, not reaching posteriorly to the cardinal process. 
Adductor field small. 
Genotype.—Glyptambonites musculosus Cooper, new species. 
Discussion.—The shells of Glyptambonites are unusually beautiful with their 
varied radial costellae and the oblique wrinkling of the hinge. The genus also 
attains a large size for an early Paleozoic brachiopod. The interior details are 
similar to those of Palaeostrophomena but the habit and profile are different from 
those of that genus, which has a resupinate lateral profile. 
Although the interior details are like those of Palaeostrophomena, some fea- 
tures are differently developed than in that genus. The diductor scars are usually 
much longer and more slender than in Palaeostrophomena. The adductor field 
is enclosed deeply by the diductors, and the space between the diductors and 
anterior to the adductor field is occupied by a longitudinally striated and granu- 
lose area. The ovarian impressions are not as proportionately large as those of 
Palaeostrophomena. Inside the brachial valve the brachiophores are more deli- 
cate than those of Palaeostrophomena and the adductor field is smaller. The 
pallial marks of both valves are similarly arranged to those of Palaeostrophomena. 
GLYPTAMBONITES GLYPTUS Cooper, new species 
Plate 168, A, figures 1, 2; plate 173, C, figures 13-23; plate 175, A, figures 1-8 
Shell semielliptical in outline, wider than long, thin, concavo-convex. Lateral 
margins slightly rounded; anterior margin broadly rounded. Cardinal extremi- 
ties narrow acute to mucronate in the young but only slightly auriculate in the 
adult and old shells. Surface ornamented by costellae of different sizes, from 5 
to 7 of the stronger costellae mark the umbonal region and the young stages, but 
in growth, costellae of intermediate size are intercalated between the primary 
ones and the finest costellae, covering the whole surface. Total strong costellae 
at the front margin about 20. Median costella usually the strongest of them all. 
Very fine costellae from 5 to 7 in a millimeter occupy the spaces between the 
stronger ones. Very fine concentric fila cancellate the fine costellae. Postero- 
lateral region marked by strong oblique wrinkles and in the posterior quarter to 
half of the valves transverse wrinkles may undulate the sectors of shell marked 
out by the major costellae, these portions of the valve often suggesting the genus 
Ptychoglyptus in ornamentation. 
Pedicle valve very slightly convex in lateral and anterior profiles. Central and 
posteromedian parts of the valve slightly swollen but the anterior, lateral, and 
