PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 485 
Horizon and locality—Valcour formation in New York: On Valcour Island, 
Lake Champlain, Plattsburg (15’) Quadrangle. 
Discussion.—This is a fairly large species characterized by a nearly recti- 
marginate anterior commissure, sulcate brachial valve, and numerous costellae. 
The species is somewhat more strongly costellate than the Southern Appalachian 
species but is more finely costellate than the common New York M. vulgaris. It 
is also larger than that species and M. nucleoidea. It suggests M. extensa in 
ornamentation but has a much narrower hinge. 
MIMELLA TUMIDA Cooper, new species 
Plate 80, B, figures 15-23 
Shell fairly large for the genus, wider than long; subrectangular in outline; 
sides moderately rounded; anterior margin broadly rounded; anterior commis- 
sure gently uniplicate ; hinge equal to about two-thirds the width; cardinal ex- 
tremities obtusely rounded; greatest width near the middle. Multicostellate, 
costellae narrowly rounded, somewhat crowded, often fasciculate on parts of the 
shell, about 2 to the millimeter at the front margin of an adult. 
Pedicle valve fairly strongly convex in lateral profile with most of the con- 
vexity in the posterior half and with the front half somewhat flattened ; anterior 
profile fairly strongly convex and forming a dome with fairly steep sides. Um- 
bonal region somewhat narrowly swollen; posteromedian region gently swollen 
and with long, steep slopes to the cardinal extremities; anterior half somewhat 
flattened and in the median region along the margin depressed into a shallow 
sulcus. Interarea curved, apsacline ; beak incurved. 
Brachial valve in lateral profile fairly strongly convex, the posterior part the 
most convex; anterior profile strongly convex and forming an arch highest in 
the middle and with long, steep lateral slopes. Umbonal region inflated and 
somewhat elevated posterior to the posterior margin; median region swollen; 
anterior somewhat flattened. Interarea strongly curved over the pedicle inter- 
area; beak prominent. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
PIoloty perce. oe elie outs os 21.5 21.0 24.9 16.7 14.8 
Paratype (llO730)))) es: ceeialels 13.6 12.9 16.3 13.6 9.2 
Types.—Holotype: 110714; figured paratype: 110739. 
Horizon and locality—Lincolnshire formation (Hogskin member) in Ten- 
nessee: # mile southwest of Washburn, Dutch Valley (T.V.A. 154-SE) Quad- 
rangle; Maynardville Pike, 1.7 miles north of Hall Crossroad, Fountain City 
(T.V.A. 146-SW) Quadrangle; Evans Ferry, Howard Quarter (T.V.A. 
162-NW) Quadrangle; 44 miles west-southwest of Thorn Hill, Avondale 
(T.V.A. 162-SW) Quadrangle. 
Discussion—This species is like M. globosa and approaches that species in 
size, although the biggest specimens of M. tumida are smaller than the largest 
