Fauna of the Morroiv Group 
141 
their middle points. Zooecia roughly arranged in diagonally 
intersecting series with 10 or 11 apertures in 5 mm. ; aper- 
tures small but surrounded by thick and strongly elevated peris- 
tomes with walls approximately as thick as half the diameter 
of the apertures; apertures sub-oval or sub-circular in outline, 
normally about 0.2 mm. in diameter. Surface of frond between 
the apertures and within the dimples very finely rugose. 
Remarks. Among the previously described representatives 
of this genus, all of which are reported from Mississippian 
strata, the material in hand is most nearly related to G. keyser- 
lingi and G. elegans. It is clearly distinguished from those 
forms by the thick-walled and strongly elevated peristomes and 
the wider spacing of the zooecial apertures as well as by the 
absence of the peripheral ridges surrounding, more or less com- 
pletely, the dimples of the zoaria referable to those species. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Station 135). Morrow formation: near Ft. 
Gibson, Oklahoma (Stations 296 and 301). 
BRACHIOPODA 
DISCINIDHG 
Genus ORBICULOIDEA D’Orbigny 
Orbiculoidea minuta n. sp. 
Plate VIII, figures 2, 2a. 
Description. Shell very small, sub-circular in outline. Di- 
mensions of the type, a brachial valve : length, 3.3 mm. ; width, 
3.4 mm. ; convexity, about 0.6 mm. 
Pedicle valve nearly flat, pedicle opening excentric, external 
surface marked by regular concentric lines of growth. 
Brachial valve depressed conical, the apex situated at about 
one-fourth the diameter of the shell from the posterior margin, 
the surface sloping with little or no curvature from apex to 
posterior margin, but distinctly, though slightly, concave from 
apex to anterior margin. Surface marked by fine, rounded, some- 
what irregular, concentric lines of growth which are a very 
little elevated above the surface. 
Remarks. This species is characterized by its small size and 
the concave anterior slope of the brachial valve, a character 
