PART IT CHAZYAN AND RELATED BRACHIOPODS—-COOPER 381 
Growth.—A series of 25 specimens ranging in size from 1.75 mm. in length 
by 2.5 mm. in width to 15 mm. long by 19 mm. wide shows a progressive length- 
ening of the shell. The largest specimen in the collection shows that this length- 
ening has been carried so far that old adults have the length and width almost 
equal. The youngest specimen shows 12 primary costellae and the intercalation 
of the second generation. 
Horizon and locality—Wardell formation in Virginia: At Rye Cove and its 
immediate vicinity, Clinchport (T.V.A. 188-NW) Quadrangle. 
Discussion.—Except for G. assimuilis this species attains the largest size of any 
Glyptorthis encountered in the rocks studied. G. virginica can be recognized 
by the fact that the pedicle and brachial beaks have about the same distance from 
the margins which gives the valves approximately the same length/width ratio. 
In some specimens the brachial length actually exceeds that of the pedicle valve, 
but usually the pedicle valve is slightly longer than the other. Features that will 
help in recognition of G. virginica are the rectangular form, the convex umbonal 
regions, and the broad, shallow sulcus. G. virginica is very close to G. assimilis 
but differs in having a more transverse outline and more subdued ornamenta- 
tion. Only in extreme cases do the proportions of G. virginica approach those 
of G. assimilis. 
GLYPTORTHIS sp. 1 
Plate 46, A, figures 1-4 
This is probably a new species represented by a fine pedicle valve and a crushed, 
immature complete specimen. Pedicle valve somewhat rectangular in outline; 
cardinal extremities forming a right angle; sides nearly straight and perpendicu- 
lar to the hinge; posterolateral extremities narrowly rounded; anterior margin 
gently rounded ; interarea nearly catacline, not curved ; teeth small; lateral plates 
well developed; dental plates short and receding; muscle area with prominent 
wide diductor scar and a narrow, linear adductor track elevated anteriorly and 
with a short median ridge anterior to it. Lateral and anterior profiles gently 
convex. 
Surface marked by about 37 narrowly rounded to subangular costellae sepa- 
rated by striae equal to or slightly less than the width of adjacent costellae ; im- 
brications broad, about 3 to the millimeter. 
Measurements in mm.—116948, length 9.2, width 10.8, hinge width 9.8, thick- 
ness 3.6. 
Figured specimen.—1 16948. 
Horizon and locality—Dark shale just below Eureka quartzite in Nevada: 
North-facing nose of hill 8167, Martins Ridge, Monitor Range, Roberts Moun- 
tains (1°) Quadrangle. 
Discussion.—The subquadrate outline and inflated pedicle valve are not like 
any other described in this report. In absence of the brachial valve it is inadvisa- 
ble to use a new specific name. 
