BART NE CHAZYAN AND RELATED BRACHIOPODS—COOPER 715 
closely spaced strong costellae in the adult stages and the wrinkling on the pos- 
terior margin is strong and extends along nearly the entire shell width. 
GLYPTAMBONITES MUSCULOSUS Cooper, new species 
Plate 171, B, figure 15; plate 175, B, figures 9, 10; plate 175, C, figures 11-13; 
plate 176, A, figures 1-5 
Shell large, plano- to concavo-convex, with the hinge forming the widest part; 
sides gently rounded and sloping inward somewhat obliquely ; anterior margin 
broadly rounded. Cardinal extremities acute to mucronate. Posterior margin 
nearly straight. Surface finely costellate, costellae of two sizes and consisting of 
large primary and secondary, tertiary and quaternary costellae in a mat of ex- 
tremely fine costellae. Five or six of the larger costellae occupy a space of 5 mm. 
at the front of a valve 19 mm. long. Fine costellae cancellated by moderately 
strong concentric fila. Posterior margin and umbolateral slopes strongly wrinkled. 
Pedicle valve evenly and faintly convex in anterior and lateral profiles; umbo 
and median regions faintly swollen; area in front of cardinal extremities gently 
concave. Interarea about twice as long as the brachial one; pseudodeltidium 
narrowly swollen. 
Interior with elongate diductor scars extending nearly to the middle of the 
valve ; adductor impressions forming a small oval patch located in the apical angle 
formed by the long diductors ; area immediately anterior to adductor scars and 
between diductors strongly granulose; teeth moderately strong, double as in 
Palaeostrophomena; false dental plates thick; ovarian impression a triangular 
area of wavy lines and granules in the angle formed by the palintrope and the 
false dental plates. Pallial marks prominent, the trunks narrow and numerous, 
each trunk formed of two channels, thin and deep, separated by a low ridge. 
Complete brachial exterior not yet known but a single impression of the 
brachial interior indicates a nearly flat valve with hypercline interarea and nar- 
rowly elevated chilidium. Interior with short and delicate brachiophores partially 
buried in the tissue of the notothyrial platform ; cardinal process with short shaft, 
bulbous at its posterior end and with triseptate myophore, the median ridge of 
which is strongly elevated, adductor field forming an inverted pentagon bisected 
by a moderately strong but low median ridge; anterior adductors smaller than 
the posterior pair and forming the apex of the pentagon. Pallial marks promi- 
nent, two trunks coming off the inside ends of the anterior adductors and ex- 
tending anteriorly along each side of the median ridge; a second pair of trunks 
originates at the line of junction of the adductor scars and extends anterolaterally. 
Ovarian impressions moderately large. 
Measurements in mm.— 
Hinge 
Length Midwidth width 
Piolotyme wees. boy. eleteos ye Oath ho OY, SIR 25.4 33.2 37.0+ 
Patat wpe CLE 7 SOO). 6 ids sy sie os ajee vive ceecs on 18.7 26.0 35.0 
4 CES PaBS Ee Se ce arte stew led on clareels 17.6 24.5 27.0+ 
