PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 203 
LINGULELLA RIDEAUENSIS Cooper, new species 
Plate 5,1, figures 26-31 
Shell thin, of about medium size for the genus, oval in outline, dark brown 
or black in color. Beak pointed, posterolateral margins straight and forming an 
angle of about 90° with the beak. Widest slightly anterior to the middle. Lateral 
margins broadly rounded; anterior margin gently rounded, forming narrowly 
rounded anterolateral extremities. Valves subequal in depth. Surface marked 
by unevenly spaced, elevated concentric lines crowded in the posterolateral re- 
gions, more distant in the median area. 
Pedicle valve unequally convex with the maximum depth at about the middle ; 
anterior slope long and gentle; umbonal and median regions swollen; lateral 
slopes moderately steep, short, extending anteriorly nearly to the anterolateral 
margins. 
Brachial valve swollen in the umbonal and median regions, the swelling ex- 
tending anteriorly to a point anterior to the middle; lateral profile strongly ele- 
vated in the median half, sloping in the posterior and anterior quarters ; anterior 
slope short but fairly gentle. Anterior and posterior profiles broadly rounded 
in the median region with short, moderately steep lateral slopes. Beak bluntly 
pointed, not protruding posterior to the posterior margin. 
Measurements in mm.— 
Length Width Thickness 
Holotype (pedicle valve) ................6 13.5+ 10.6 1.0? 
Paratype (brachial valve 109315a) ......... 15.6 12.0 ? 1.6? 
Types.—Holotype: 109315c; figured paratypes: 109315a,b, 109324a,c; un- 
figured paratypes: 109324b. 
Horizon and locality—Aylmer formation (Rockcliffe member) in Canada: 
Hogs Back on Rideau River south of Ottawa, Gloucester Township, Carleton 
County, Ontario; 44 miles west of Ottawa, Ontario. 
Discussion—This species is characterized by its thin shell, oval outline, and 
exterior marked by concentric undulations only. It suggests L. brainerdi, but 
that species generally attains a larger size than the Canadian species and is more 
quadrate in outline. Lingulella? huronensis is of about the same size but is less 
attenuated. 
LINGULELLA RUGOSILINEA Cooper, new species 
Plate 4, D, figures 14-16 
Shell small, longer than wide, ovate in outline with gently convex lateral 
margins. Anterior margin gently rounded; anterolateral extremities broadly 
rounded. Pedicle beak bluntly pointed, forming an angle of about 100°. Beak 
of brachial valve marginal, forming an angle of about 110°. Surface ornamented 
by fine irregular radial striae between which are located fine concentric wrinkles 
concave posteriorly and ending laterally against the striae. Radii lost near the 
margins where wavy concentric lines make the ornament. 
Measurements in mm.—Holotype, length 12.5, width 7.3. 
