648 THE PALEONTOLOGY OF MINNESOTA. 



Ll'rimltiella 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 abroad, 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. 



I'riiiiitiella elongata, var. nudu Jones,* is similar but has straighter ends and 

 sharper dorsal angles. 



Formation and locality. Lower and upper Birclseye limestone. High Bridge, Kentucky, and Leba- 

 non and Lavcrgne, Tennessee; lower third of the Trenton shales, Minneapolis, St. Paul, and Goodhue 

 county, Minnesota. 



PRIMITIELLA LIMBATA, n. sp. 



PLATE XL1II. FIGS. 63-56. 



SI/K. (E. C.) Length 0.73 mm.; bight 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 sliales, Minneapolis, Minnesota. 



PKIMITIELLA SIMIILANS, n. sp. 



PLATE XLIII, FIGS. 26-28. 



SIX.E. Length 0.73 mm.; bight 0.44 mm.; thickness 0.28 mm. 



Valves rather strongly convex, leperditoid in outline, with the dorsal 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 

 xul,(,r<itits and /^im/itoides Jones. Still it is relatively higher than any of these, and 

 the last two are without the dorsal depression. It 'resembles also A. minutissimus 

 Iliill, I nit may be distinguished by its proportionally greater length. 



f'oriiiittiiin a,,<l locality.- Lower p:irl. of t.he Trenton shales, near Fountain, Minnesota. 



'' r "' lllU '<"' "-, ii varlel.v "f l',iniili'i ilnnunl'i Kniuw, Inn sinre Ilr. Kransc ha- shown that, hi* 



' atnl fal-i- bonier Ukf that of Kinwliiliiin lutafriafci llricli, tin? form multi should now lie 

 iiy.-imi probably generlo&llj dlittnot from/- a,,,, 



