PLATE XXXII. 
Paok. 
Figs. 1 to 5. Lept^^na ciiAKLonMo W. and S 410 
1 and 2. Views of tlie ventral and dorsal valves respectively of an entire specimen, show- 
ing the zigzag surface ornamentation and the deflected anterior margin. 
3. Profile outline of the same specimen. 
4. Interior of the dorsal valve of a similar specimen. Collection of G. Schuchert. 
.5. Interior of a ventral valve. Trenton shales, St. Paul, Minn. Minnesota Geo- 
logical Survey collection. 
Figs. 6 to 9. Lept^na iinicostata Meek and Worthen, sp 411 
6 and 7. An exterior view of the ventral valve and a profile outline of the same specimen. 
Minnesota Geological Survey collection. 
8. Interior of the ventral valve, showing the adductor and the elongate diductor 
muscle scars and the strongly tuberculose surface. 
9. Interior of the dorsal valve, which is much as in L. kiiomboidalis, var. tenui- 
striata. Hudson Rivergroup, Spring Valley, Minn. Collection of C. Schuchert. 
Figs. 10 to 12. Pi.EC'TAMBONiTES SERiCEA Sowcrby, sp 414 
10. A view from the dorsal valve of a specimen from the Hudson River group of Ohio. 
D, deltidium. (After Hall.) 
11. Interior of the dorsal valve of another specimen from the same locality, a, 
adductor muscle scars; c, crural plates; ./, cardinal process: v, vascular impres- 
sions. (After Hall.) 
12. Interior of a ventral valve to show the crenulated hinge margin and the muscular 
scars. Hudson River group, Granger, Minn. Minnesota Geological Survey 
collection. 
Figs. 13 to 17. Plectambonites gibbosa W. and S 41G 
13, 14 and 15. Ventral, dorsal and profile views respectively of an entire specimen, x 2. 
16 and 17. Dorsal and ventral valve interiors, drawn from gutta percha impressions made 
from natural casts. Middle Galena, near Cannon Falls, Mantorville and Old 
Concord, Minn. Minnesota Geological Survey collection. 
Figs. 18 to 23. Orthis tricenaria Conrad 418 
18, 19 and 20. Dorsal, ventral and profile views of a specimen wider than is common for the 
species. Minnesota Geological Survey collection. 
21 . The interior of a well preserved dorsal valve. University of Minnesota collection. 
22. An interior of the ventral valve. 
23. A cardinal view to show the small deltidia on both valves, and the chilidiura of 
the dorsal valve, x 2. Trenton shales, Minneapolis, Minn. Collection of C. 
Schuchert. 
Figs. 24 to 30. Orthis (Dikorthis) deflecta Conrad, sp 422 
24 and 25. Exterior and interior views of a ventral valve. (Fig. 24 after Hall.) 
26. The interior of a dorsal valve. (After Hall.) Trenton limestone, near Fountain, 
Minn. 
27, 28 and 29. Ventral, dorsal and cardinal views of a rather thick specimen. (After Hall.) 
Trenton limestone, Minneapolis, Minn. Collection of C. Schuchert. 
30. Profile outline of another specimen. Lower Blue beds, Janesville, Wis. Minne- 
sota Geological Survey collection. 
Figs. 31 to 34. Orthis (Dinorthis) pectinella Emmons 424 
31. ^The interior of the ventral valve of the type sp-^cimen of O. charlotta; Winchell. 
The outer margin of the shell is slightly broken. Trenton shales, Minneapolis, 
Minn. Minnesota Geological Survey collection. 
32 and 33. Dorsal valve and profile outline of another specimen. 
34. Cardinal view of the dorsal valve of a smaller specimen, to show the small del- 
tidium. Trenton shales, St. Paul, Minn. Collection of C. Schuchert. 
Figs. 35 to 38. O. (D.) pectinella, var. swebneyi N. H. Winchell 426 
35 and 36. View from the dorsal valve and profile of same specimen. (Fig. 35 after Hall.) 
37 and 38. Interiors of the dorsal and ventral valves. (After Hall.) Trenton shales, St. 
Paul, Minn. Collection of C. Schuchert. 
Figs. 39 to 42. Orthis (Dinorthis) meedsi W. and S 427 
39 and 40. Dorsal and cardinal views of a specimen in which the striae are separated more 
than is usual. 
41 and 42. Ventral and profile views of a larger specimen. Galena shales, Kenyon, Minn. 
42a. Cardinal view. Collection of W. H. Scofleld. 
