646 THE PALEONTOLOGY OP MINNESOTA. . ,. 



LAparchites arreotiis. 



The peculiar fringe distinguishes this species from all the Lower Silurian Ostra- 

 coda know to me. 



Formation and locality.— HuHsoa River group, near Spring Valley, Minnesota. 



APAKCHITES ARBBOTUS, tl. Sp. 

 PLATE XLin, FIGS. 35 and 36. 



Size.— (R. V.) Lengtli 0.81 mm,; hightO.53 mm.; thickness 0.11 mm. 



Valves compressed-convex, scarcely if at all oblique, semiovate, the ends almost 

 vertical in the upper half, the dorsal edge straight and very long; greatest convexity 

 in the lower part of the valves, a large portion of the central part of the surface 

 appearing flattened; free margins minutely toothed; bevel very narrow. 



The dentate margin reminds of A. grariilabiatus, but as the present form is much 

 smaller and not nearly so convex, and as it has a longer hinge line and is much more 

 elongated, it is quite evident that we are dealing with a distinct species. Its smaller 

 size, erect ends and dentate margins distinguish it from A. millepundatus. 



Formation and locality .—JJjiT^er third of the Trenton shales, St. Paul, Minnesota. 



Aparchitbs ohatfieldensis, n. sp. 



PLATE XLIII, FIGS. 37 and 38. 



Size.— (L. V.) Length 0.76 mm.; hight 0.46 mm.; thicliness 0.j2 mm. 



Valves compressed-convex, somewhat elongate leperditoid in outline, being 

 widest posteriorly; hinge line long, straight, dorsal angles rounded; posterior outline 

 peculiar -in swinging forward more than backward; ventral edge narrowly beveled 

 inward; surface not well preserved but retaining some evidence of having been 

 obscurely pitted. 



The posterior outline is different and the thickness of the carapace less than in 

 any other of the elongate species of the genus so far described. 



Formation and locality. — Middle third of the Trenton shales, Chatfleld, Minnesota. 

 ApAECHiTES MINUTI8SIMUS Hall, var. TRBNTONENSis, «, var. 



PLATE XLIII, FIGS. 18-20. 



Leperditia (IsocMlina) minutissimaJlX'LL,, 1871, Desc. N. Sp. Eoss. Hud. Eiv. Gr., p. 7; also 1872, 24th 



Rep. N. Y. St.Mus. Nat. Hist., p. 231, pi. 8, flg. 13; Hall and Whit- 

 field, 1875, Pal. Ohio, vol. ii, p. 102. 



Aparchites minutissimus Uleich, 1889, Contri. Can. Micro-Pal., pt. 2, p. 49. 



Size.— (R. V.) Length 0.85 mm.; hight 0.54 mm.; thickness 0.16 mm. 

 (R. V.) " 0.49 " " 0.33 '' 



Two right valves of the Trenton variety of this species are figured on plate 43. 

 The anterior part is narrower and the dorsal angles duller tha,n iu tbe typical Cin- 



