PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 655 
anterolateral margins narrowly rounded; anterior margin broadly rounded; sur- 
face marked by rounded costae: 4 to 7 on the fold, 3 to 6 on the sulcus, and 5 to 
8 on the flanks. 
Pedicle valve with lateral profile fairly evenly and moderately convex ; anterior 
profile broadly and gently convex; umbonal and median regions somewhat nar- 
rowly swollen; sulcus originating at the middle, shallow and wide; tongue 
broadly rounded but fairly short. Flanks narrowly rounded, with steep sides. 
Brachial valve moderately convex in lateral profile, fairly strongly convex in 
anterior profile; umbonal and median regions moderately swollen; sulcus origi- 
nating at about the middle, low throughout its length and not markedly differ- 
entiated from the flanks which are swollen and have steep slopes to the margins. 
Measurements in mm.— 
Brachial Max. 
Length length width Thickness 
AAU os, o sia\eic-01s on s)ae se saw dee 8.6 78 9.5 5.2 
aGAEU DE LE Tae AOD) cee cee s,s a scons 9.0 8.2 8.90 6.4. 
HS GUE7Z238C) Is cueau"s sea once 0.5 8.7 9.9 6.2 
S GRITII0) scale te ou nede 0.1 8.2 0.1 5.3 
* MPTP SI0E) choos cscs e wwe 7.8 7.2 7.8 4.5 
Types.—Holotype: 117238; figured paratype: 117238b; unfigured paratypes: 
117238c-e. 
Horizon and locality—Lenoir formation (Douglas Lake member) in Ten- 
nessee: 0.65 mile southwest of Williamson Chapel, Tallassee (T.V.A. 139-SE) 
Quadrangle. 
Discussion—This species is characterized by moderate size, nearly equal 
length and maximum width, wide fold and sulcus, and numerous costae. Al- 
though it suggests R. raymondi, that species is much more strongly costate. 
Rostricellula basalaris occurs at about the same level but is more triangular in 
outline and is somewhat more strongly costate. Rostricellula multicostata also 
occurs at the same level, but it is much larger and has a more pronounced fold 
which is marked by about the same number of costae as in the Tennessee species. 
However, the Virginia species has more costae on the flanks than the Tennessee 
form. 
The base of the Lenoir or its equivalent in many places in the Appalachian 
Valley is marked by abundance of Rostricellula. Often the rock is so filled with 
these rhynchonellid shells that no other species are to be found. It is odd that 
from place to place these shells seem to vary specifically. They were undoubtedly 
controlled by environmental conditions that varied geographically. Evidence of 
such geographic variation is encountered also in other places and other strata 
and will one day form a fruitful subject for investigation. 
ROSTRICELLULA WILSONAE Cooper, new species 
Plate 135, F, figures 36-48 
Shell of about medium size for the genus, slightly wider than long, sides nar- 
rowly rounded and greatest width just anterior to the middle. Apical angle ap- 
