Geology of tJic St. Croix Dalles. — Berkey. 281 
Tryblidium barabuensis (Whitfield.) 
Metoptoina barabuensis Whitfield. Ann. Rept. Wis. Geol. Survey for 
1877, p. 60, 1878. 
Metoptoina barabuensis^\\\\.'a.^\(S.. Geol. Wis., vol. iv, p. 195. 1882. 
Metoptoma ba/-aduensis Sardeson. Minn. Acad. Nat. .Sciences, vol. 
IV, part I, p. 97, 1896. 
Plate XX, Fitfs. 18 and 19. 
It was first thought that the form described as T. convexiim above 
was identical with Metoptoina barabuensis of Whitfield, but the fol- 
lowing points of difiference were considered of too much importance for 
such identification: 
The apical angle of T. barabuensis is 70° : the apex also falls outside 
of the anterior margin, and the posterior slope is quite convex, while 
the anterior slope is slightly concave. A specimen collected and identi- 
fied by Dr. Sardeson from Osceola conforms closely to this type, dif- 
fering chiefly from Whitfield's specimen in the less broadly oval outline 
of the aperture and the rather strongly developed growth plications. 
Formation and locality: The Jordan sandstone, Osceola, Wisconsin. 
Tryblidium extensum, n. sp. 
Plate XX, Figs. 16 and 17. 
Conical shell, inclined far forward so as to project considerably be- 
yond the anterior margin; greatest hight of shell at a point immediately 
over the anterior margin, equal to 10 mm.; aperture is broadly oval, 
slightly acuminate anteriorly; posterior slope uniformly more convex 
than T. barabuensis ; anterior slope strongly concave; surface closely 
concentrically striated; length 20 mm.; apical angle about 40°; distance 
from the posterior margin to apex 26 mm. 
This specimen is defective, but is sufficiently complete to allow res- 
toration of all missing parts. It forms an important step in the mor- 
phologic series. 
Formation and locality: Dresbach. Found at Taylor's Falls in the 
conglomerate. 
This species is similar in general form to /'. exsertinn .Sardeson 
[Stcnotheea exserta Llrich) from the Trenton, although it is very dif- 
ferently marked and less acute at the apex. 
Tryblidium corpuletitum, n. sp. 
Plate XX, Fitrs. "il ixwKTL 
Shell small, conical; apex obtuse and inclined beyond the anterior 
margin; posterior slope very convex; anterior slope concave; aperture 
broadly oval, nearly circular, surface smooth. The convexity of the 
sides gives this form a decidedly plump appearance. The relative width 
is much greater than in any. of the closely related species. It resembles 
some described species of Stenotheca, but the gradation from this species 
to the next one, which is clearly of the Trybliitiuni type, is so complete 
in the specimens at hand that I have no hesitation about its position. 
Highest part of shell a little forward of the middle, 6 mm.; hight of 
