PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 537 
The shell is swollen on the flanks and in the median region just posterior to the 
point where the fold originates. The specimen is unfortunately incomplete. Pos- 
sibly two distinct species are represented by the material. 
Figured specimens.—117096a-c ; unfigured specimen: 117096d. 
Horizon and locality —Sevier formation (at the top of sandstone number 5) 
in Tennessee: 0.28 mile northwest of Fourmile Church, Tallassee (T.V.A. 
139-SE) Quadrangle. 
Genus TRIPLESIA Hall, 1859 
Triplesia Hatt, Pal. New York, vol. 3, p. 522, 1859—U.Lricu and Cooper, Journ. Paleont., 
vol. 10, No. 5, p. 345, 1936. 
This genus is rare in most of the strata embraced by this book and from most 
of the geographic areas. It is commonest in the Rockland (Napanee member) 
of the Trenton group of New York where it has long been known. No authentic 
specimens of the genus have to date been taken from the Appalachians north of 
Tennessee, although it has been reported at a number of places. A well-marked 
species, however, appears in the Lebanon limestone of the Central Basin of Ten- 
nessee that had not hitherto been reported. This occurrence helps to emphasize 
the post-Black River position of this formation. A triplesid of uncertain generic 
affinities is known from the Little Oak limestone of Alabama. 
Triplesia and Onychoplecia are closely related genera, and the former prob- 
ably descended from the latter. Widening of the hinge and consequent shorten- 
ing of the pedicle beak is about all that is necessary to produce Triplesia from 
Onychoplecia. 
TRIPLESIA CARINATA Cooper, new species 
Plate 100,I, figures 41-43 
Known chiefly from the brachial valve, but a probable immature pedicle valve 
gives a clue to the generic character of the species. Large for the genus, wider 
than long ; oval in outline ; sides narrowly rounded ; hinge narrow ; anterior some- 
what trilobate. Anterior commissure deeply uniplicate with prominent brachial 
fold and deep pedicle sulcus. Surface smooth, exfoliated areas marked by distant 
costellae. 
Pedicle valve tentatively defined as having gentle lateral profile, and broad, 
gently convex anterior profile ; beak somewhat elongated ; sulcus originating near 
the middle, deep and angular in section with a deep central groove; tongue ex- 
tremely long and angular. Median region gently swollen. Sulcus bounded by 
oblique, angular plicae. Foramen small, elongate; dental plates elongate and 
narrowly divergent. 
Brachial valve forming a rounded ellipse in outline, widest at about the middle; 
lateral profile strongly convex and with greatest depth in the midregion; anterior 
profile strongly domed and with a narrow median elevation. Umbonal region 
narrow, swollen; median area inflated; fold originating on the umbo, strongly 
elevated, subcarinate in section, demarcated by an oblique groove which divides 
the narrowly swollen flanks from the steep sides of the fold. All slopes steep. 
