230 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Genus OBOLELLINA Billings, 1871 
Obolellina Bitt1ncs, Canadian Nat., n. ser., vol. 6, p. 221, 1871. ' 
Broadly oval shells suggesting Dinobolus on the exterior but with moderately 
developed broad and low platform in the pedicle valve and scarcely any develop- 
ment of a platform in the brachial valve. In any case the platforms are low and 
consist of broad thickening only, without elevation and excavation. 
OBOLELLINA CANADENSIS (Billings) 
Plate 24, E, figure 24 
Obolus canadensis Bitt1ncs, Canadian Nat. Geol., vol. 3, p. 441, figs. 20-23 (not fig. 19 = 
O. magnifica), 1848; Geol. Surv. Canada, Rep. Progress for 1857, p. 180, figs. 20-23 (not 
fig. 19), 1858; Geol. Canada, p. 142, fig. 75, 1863. 
Obolellina canadensis (Billings), Canadian Nat. Geol., n. ser., vol. 6, p. 222, 1871; ibid., 
p. 326, fig. 15, p. 320, fig. 6, 1872. 
Dinobolus canadensis (Billings) DAvipson and Kine, Quart. Journ. Geol. Soc. London, 
vol. 30, p. 162, pl. 19, fig. 7, 1874—Witson, Geol. Surv. Canada, Bull. 8, p. 16, pl. 1, 
fig. 24, 1946. 
Types.—Holotype: G.S.C. 1150; paratype: G.S.C. 1150a. 
Horizon and locality.—Leray-Rockland beds, Fourth Chute of the Bonnechére 
River, Renfrew County, Ontario, Canada. 
OBOLELLINA DIXONENSIS Cooper, new species 
Plate 22, K, figures 18-21 
Exterior of shell not known; length of beak not known; shell evidently thin. 
Valves subequally convex. Impressions of the pedicle interior indicate a trans- 
versely oval outline ; lateral margins narrowly rounded; anterior margin broadly 
rounded. Lateral and anterior profiles broadly convex and nearly equal; lateral 
slopes short and moderately steep; median region depressed convex in anterior 
profile. 
Pedicle interior with a moderately thickened, nonexcavated, diamond-shaped 
muscle area; sides of muscle area narrowly angulated in the middle; anterior 
narrowly rounded. Individual scars not clear, but a depressed track extending 
from the apex to the anterior angle suggests the growth path of 2 unidentified 
muscles. Brachial muscle platform similar in outline to the pedicle one; indi- 
vidual muscle marks not identifiable. The holotype (71814a) measures 15.2 mm. 
long by 20.3 mm. wide, representing measurement of interior surface only. 
Types.—Holotype: 71814a; figured paratype: 71814b; unfigured paratypes: 
7181 4c-1. 
Horizon and locality.—Platteville formation (just above sponge bed), Tru- 
man’s Quarry, 2 miles northeast of Dixon, III. 
Discussion—This species is suggestive of O. parva (Whitfield) from the 
Prosser limestone of Minnesota and Wisconsin but differs in being a larger and 
more tranverse shell and in lacking any trace of median septa anterior to the 
muscle platforms. 
