PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 231 
Although only internal impressions are available for study, the species is as- 
signed to Obolellina because of the modest thickening and nonexcavated char- 
acter of the muscle platforms. The species evidently is an early form of dinobolid 
in which the muscle platforms are in an incipient stage of development. 
OBOLELLINA ERECTA (Wilson) 
Dinobolus erectus Witson, Geol. Surv. Canada, Bull. 8, p. 17, pl. 1, fig. 25, 19046. 
Type.—Holotype: G.S.C. 6301. 
Horizon and locality—Leray-Rockland beds, Fourth Chute of the Bonnechére 
River, Renfrew County, Ontario, Canada. 
OBOLELLINA MAGNIFICA (Billings) 
Plate 13, A, figures 1-3; plate 24, F, figure 25 
Obolus canadensis Bittincs (part), Geol. Surv. Canada, Rep. Progress for 1857, p. 180, 
fig. 19 (not figs. 20-23), 1858; Canadian Nat. Geol., vol. 3, p. 441, fig. 19 (not figs. 20-23), 
1858. 
Obolellina magnificus (Billings), ibid., n. ser., vol. 6, p. 329, fig. 7, 1872. 
Dinobolus magnificus (Billings) Davipson and Kine, Quart. Journ. Geol. Soc. London, 
vol. 30, p. 164, pl. 19, fig. 8, 1874—NicHotson, Paleont. Province Ontario, p. 17, fig. 6, 
1875.—Witson, Geol. Surv. Canada, Bull. 8, p. 17, pl. 1, figs. 26, 27, 1046. 
Broadly oval in outline, beak somewhat pointed, forming an angle of about 
110° ; prominence of beak emphasized by a slight depression in the posterolateral 
margins. Lateral and anterior margins strongly rounded and approximately a 
circle. Valves unequally biconvex, the brachial valve having the greater con- 
vexity. Surface marked by concentric lines of growth and strong growth varices. 
Pedicle valve gently convex in lateral profile and with the greatest convexity 
in the posterior third; anterior two-thirds somewhat flattened. Anterior profile 
broadly convex with long and gentle lateral slopes. 
Brachial valve moderately and evenly convex in lateral profile; greatest con- 
vexity at about the middle; anterior profile with broadly swollen median area 
and short, moderately steep lateral slopes. Beak small, set off by short slopes ; 
beak protruding slightly posterior to the posterior margin. 
Pedicle interior with broad and shallow pedicle groove; posterior thickened 
by a broad muscle callosity extending to about the middle of the valve; muscle 
marks not preserved in the specimens at hand. 
Brachial interior with unthickened posterior margin; posterior region thick- 
ened to form a muscle platform, perforated by a deep pit at the umbo. 
Measurements in mm.— 
Length Width Thickness 
Hypotype (pedicle valve 116800a) .......... 29.2 29.0 4.5 
fs (brachial valve 116800b) ........ 23.5 28.0 4.8 
Types.—Holotype: G.S.C. 1161; paratypes: G.S.C. 1161a-d; figured hypo- 
types: 116800a,b,d; unfigured hypotype: 116800c. 
Horizon and locality —Rockland formation in Ontario, Canada: At Paquette 
Rapids ; Bonnechére River, 1 mile below Eganville. 
