648 THE PALEONTOLOGY OF MINNESOTA. 
[Primitiella limbata. 
gently convex, or almost straight in the middle; posterior margin somewhat oblique 
and subtruncate above; anterior outline always more curved than the posterior; free 
edges with a narrow border; surface with a broad, centro-dorsal depression. 
The earliest known occurrence of this species is in the lower part of the Birds- 
eye limestone of Kentucky. These specimens differ slightly from the later form in 
having the border much narrower, the ventral margin straighter and quite parallel 
with the dorsal, and the anterior outline more rounded.’ The valves seem also to 
be a little more convex. 
Primitiella elongata, var. nuda Jones,* is similar but has straighter ends and 
sharper dorsal angles. 
Formation and locality.—Lower and upper Birdseye limestone, High Bridge, Kentucky, and Leba- 
non and Lavergne, Tennessee; lower third of the Trenton shales, Minneapolls, St. Paul, and Goodhue 
county, Minnesota. 
PRIMITIELLA LIMBATA, 2. Sp. 
PLATE XLIII, FIGS. 53—56, 
SizE.—(E. C.) Length 0.73 mm.; hight 0.38 mm.; thickness 0.20 mm. 
. The outline is almost as in P. constricta, only the ends are less rounded, the 
posterior one especially being nearly vertical, while the dorsal angles are sharper. 
The most important difference however lies in the fact that the border continues 
not only around the free edges but along the dorsal margin as well. The thickness 
of the carapace is somewhat less, and the surface rises more abruptly from the 
posterior border. Finally, the mesial depression is more obscure, and often scarcely 
distinguishable. 
Formation and locality.—Lower third of the Trenton shales, Minneapolis, Minnesota. 
PRIMITIELLA SIMULANS, %. Sp. 
PLATE XLIII, FIGS. 26—28. 
SizeE.—Length 0.73 mm,; hight 0.44mm.; thickness 0.28 mm. 
Valves rather strongly convex, leperditoid in outline, with the dorsa! angles 
rounded; edges without border; a very faint, broad depression near the middle of 
the dorsal slope, and occasionally an obscure elevation at its base. 
In the outline this species is very nearly like P. minuta Eichwald and Aparchites 
subovatus and leperditoides Jones. Still it is relatively higher than any of these, and 
the last two are without the dorsal depression. It resembles also A. minutissimus 
Hall, but may be distinguished by its proportionally greater length. 
Formation and locality.—Lower part of the Trenton shales, near Fountain, Minnesota. 
*Prof. Jones describes this form as a variety of Primitia elongata Krause, but since Dr. Krause has shown that his 
species possess a radially striated false border like that of Eurychilina? sub@quata Ulrich, the form nuda should now be 
regarded as at least specifically and probably generically distinet from P elongata, 
