Page. 
Fig. 25. OrBICULOIDEA LAMELLOSA Hall (?) 364 
A dorsal valve, provisionally referred to this species. Hudson River group, 
Spring Valley, Minn. Collection of C. Schuchert, 
Figs 26 to 28. Sciiizotp-eta pelopea Billings 365 
26. A dorsal valve. 
27. A ventral valve, showing the small oval pedicle opening. Middle Galena lime- 
stone, Mantorville, Minn. Minnesota Geological Survey collection. 
28. Natural cast of the interior of the ventral valve, pa, posterior adductor scars. 
Hudson Kiver group at Spring Valley, Minn. University of Minnesota col- 
lection. 
Figs. 29 to 31. Sciiizockania FiLosA Hall 370 
29. A dorsal valve, showing the large posterior adductor scars. 
30. Profile outline of same , attached to a gastropod. Trenton limestone, Cannon 
Falls, Minn. Collection of W. H. Scofield. 
31 . A specimen in which the upper, or dorsal, valve has been removed, exposing the 
internal characters of the ventral valve, b, dorsal valve; p, ventral valve; y, 
pedicle groove; I, walls of groove: x 2. (After Hall.) Hudson River group, 
Covington, Ky. 
Figs. .32 and 33. Crania .setigera Hall 372 
32. An upper, or dorsal, valve, showing the spiniferous surface of the species. 
33. Profile view of the .same specimen. (After Hall.) Trenton limestone at Mineral 
Point, Wisconsin. 
Figs. 34 and 35. Crania granulosa N. H. Winchell 373 
A dorsal and profile outline view of the type specimen. Trenton limestone at 
Minneapolis, Minn. Minnesota Geological Survey colleetion. 
Figs. 36 and 37. Crania trentonensis Hall 374 
Dorsal and profile views of the type specimen. (After Hall.) Trenton limestone, 
Middleville, New York. 
Figs. 38 and 39. Craniella (?) ulrichi Hall 375 
38. A cast of the interior of the ventral valve, somewhat restored on the right side, 
showing the strong anterior and very obscure posterior adductor impressions, 
and the marks of the vascular sinuses. 
39. The internal cast of a dorsal valve referred to this species, showing the muscular 
scars and the sigmoid vascular impressions. (After Hall.) Trenton shales, 
Minneapolis, Minn. Collection of C. Schuchoit. 
Fig. 40. Pholidops trentonensis, var. minor, n. var 376 
A dorsal valve (?), x 3. Trenton shales, St. Paul, Minn. Collection of C. 
Schuchert. 
Fig. 41. Lingula modesta Ulrich 344 
Ventral valve of a small specimen x 4, and outline of the natural size. 
I'^ig. 42. LlNOULA CLATIIRATA, n. sp 345 
Ventral valve of an average sized specimen x 3i, and outline of natural size. 
