332 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
umbo somewhat swollen ; lateral and posterolateral slopes gently concave. Pedicle 
valve with strongly divergent dental lamellae. 
Brachial valve with lateral profile more convex than that of the pedicle valve, 
most convex in the median and umbonal region; anterior profile broadly and 
strongly convex; sulcus shallow, short and confined to the umbonal region; 
median region broadly swollen to form an ill-defined fold; posterolateral slopes 
steep and concave. 
Measurements in mm.— 
Length Width Thickness 
Lectotype (pedicle valve 550b)............... iret 11.4 1.9? 
Paratype (brachial valve 559)..........e000. 7.9 12.7 2.0 
Types.—Lectotype: G.S.C. 559b; paratype: G.S.C. 559; figured hypotypes: 
116842a,b, 116843. 
Horizon and locality.—Table Head series in Newfoundland: Portland Creek ; 
Table Point, Table Point Cove. 
Discussion.—This species is characterized by its small size and the finely 
costellate exterior. In these respects it differs from all other described forms of 
this genus. 
PLEURORTHIS TRITONIA (Billings) 
Plate 31, F, figures 28, 29 
Orthis tritonia Bituincs, Geol. Surv. Canada, Paleozoic fossils, vol. 1, p. 76, fig. 69 (adv. 
sheets, 1862), 1865.—HaLL and Ciarke, Pal. New York, vol. 8, pt. 1, p. 217, pl. 7A, 
figs. 12, 13, 1892, 
Orthis ? tritonia (Billings) Utricn and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 103, 
pl. 18C, figs. 12, 13, 1938. 
Types.—Holotype: G.S.C. 807. 
Horizon and locality—Probably of the age of the youngest boulders of the 
Mystic Conglomerate in Limestone No. 2, Lévis, Quebec, Canada. 
PLEURORTHIS sp. 1 
Plate 32, A, figure 1 
Shell of about medium size for the genus; subelliptical in outline; sides 
rounded; anterior margin broadly rounded; surface marked by fairly coarse 
costellae arranged in bundles of 3 at the anterior margin and with about 3 to the 
millimeter. 
Pedicle valve moderately convex; greatest convexity in the umbonal region; 
anterior profile somewhat triangular with the median region swollen and some- 
what narrowly rounded and the slopes flat, long, and moderately steep; fold 
not well defined anteriorly ; sulcus not well defined. 
Brachial valve moderately convex with the greatest convexity in the median 
region; anterior profile broadly convex, depressed medially by the narrow sul- 
cus; umbo sulcate; sulcus disappearing in the median swelling; fold ill defined. 
