646 THE PALEONTOLOGY OF MINNESOTA. 
{Aparchites arrectus. 
The peculiar fringe distinguishes this species from all the Lower Silurian Ostra- 
coda know to me. 
Formation and locality.x—Hudson River group, near Spring Valley, Minnesota. 
APARCHITES ARRECTUS, #. Sp. 
PLATE XLIII, FIGS. 35 and 36. 
Sizz.—(R. V.) Length 0.81 mm,; hight 0.53 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. granilabiatus, but as the present form is much 
smaller and not nearly so convex, and as it hasa 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. millepunctatus. 
Formation and locality.—Upper third of the Trenton shales, St. Paul, Minnesota. 
APARCHITES CHATFIELDENSIS, . Sp. 
PLATE XLIII, FIGS. 37 and 38. 
SizzE.—(L. V.) Length 0.76 mm.; hight 0.46 mm.; thickness 0.12 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 shaies, Chatfield, Minnesota. 
APARCHITES MINUTISSIMUS Hall, var. TRENTONENSIS, 7. var, 
PLATE XLIII, FIGS. 18—20. 
Leperditia (Isochilina) minutissima HALL, 1871, Desc. N. Sp. Foss. Hud. Riv. Gr., p. 7; also 1872, 24th 
Rep. N. Y. St. Mus. Nat. Hist., p. 231, pl. 8, fig. 13; HALL and WHIT- 
FIELD, 1875, Pal. Ohio, vol. ii, p, 102. 
Aparchites minutissimus ULRICH, 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.) # O79) ss SCPOFSoLE 
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 than in the typical Cin- 
