PLATE XXXIV. 
Page. 
Figs. 1 to 8. Rhynchotrema ainsliei N. H. Wiachell 4.59 
1 and 2. Views of the dorsal and ventral valves of a t3 pical example. 
3 and 4. Profile and anterior views of the same specimen. Near Lanesboro, Minn. Min- 
nesota Geological Survey collection. 
5, 6 and 7. Dorsal, ventral and profile viws respectively of an immature specimen, x 2. 
8. The same specimen, natural size. Trenton shales, Minneapolis, Minn. Minne- 
sota Geological Survey collection. 
Figs. 9 to 25. Rhynchotrema in^quivalvis Castelnau 459 
9, 10 and 11. Dorsal, ventral and proflle views respectively of a specimen from the Trenton 
limestone and approaching R. orientalis Billings, x 2. 
12. A view from the dorsal valve of a strongly lamellose variety of this species 
occurring in the Clitarabonites beds, x 2, St. Paul, Minn. 
13 and 14. Ventral and profile views of the same specimen, natural size. 
15, 16 and 17. Three views, a ventral, dorsal and profile respectively, of another variety found 
in the middle third of the Trenton shales. Collection of G. Schuchert. 
18 and 19. Two views, ventral and proflle, of a thin immature specimen. Fountain, Minn. 
20,21, 22 and 23. Dorsal, ventral, proflle and anterior views respectively of a large but typical 
specimen of this species. Trenton shales, Minneapolis, Minn. Minnesota 
Geological Survey collection. 
24. An interior view of the ventral valve showing the muscular scars and teeth, x 2. 
25. The interior of the dorsal valve to show the crural plates, linear cardinal pro- 
cess and the adductor muscular scars. Near the top of Trenton limestone, 
Burgin, Kentucky. Collection of C. Schuchert. 
Figs. 26 to 29. R. iN.EQTJiVALvis var. LATicosTATA W. and S -161 
26 and 27. Dorsal and ventral views of a very characteristic specimen showing the prom- 
inent lateral costa?. 
28 and 29. Proflle and anterior views of the same specimen. The latter shows the flattened 
anterior margin, which is often well developed in this variety. Galena shales 
near Cannon Falls, Minn. Collection of C. Schuchert. 
Figs. 30 to 34. Rhynchotrema capax Conrad, sp 462 
30, 31 and 32. Three views of a large matured specimen. 
33. A broken dorsal valve, showing the crural plates surrounding the cardinal 
process, the prominent mesial septum and the adductor scars on each side of 
it. Hudson River group, Spring Valley, Minn. Minnesota Geological Survey 
collection. 
34. The interior of a very thick ventral valve. Hudson River group. Iron Ridge, 
Wisconsin. Minnesota Geological Survey collection. 
Figs. 35 to 37. Rhynchonella '? neenah Whitfleld 465 
Dorsal, anterior and proflle views of the type specimen. (After Whitfleld.) 
Hudson River group, Delafleld, Wisconsin. 
Figs. 38 to 41. Zygospira recuryirostra Hall, sp 466 
38, 39 and 40. Three views of a typical e&^mple of this species, x 2. Galena shales near 
Cannon Falls, Minn. Minnesota Geological Survey collection. 
41. A specimen filled with crystalline calcite, showing the spirals and the connecting 
band. The latter is drawn wrongly, the point of attachment of the loop is 
nearer the anterior recurved portion of the primary lamellje. x 4. Collection 
of C. Schuchert. 
Figs. 42 to 44. Zygospira modesta (Say Ms.) Hall 467 
42, 43 and 44. Dorsal, ventral and proflle views respectively of a specimen in which the sinus 
and fold are not so prominent as in Ohio valley specimens. Hudson River 
group, Spring Valley, Minn. Collection of C. Schuchert. 
Figs. 45 to 48. Zygospira uphami W. and S 4(58 
45 and 46. Ventral and proflle views of a typical example. 
47. View from the dorsal valve of the same specimen, x 2. 
48. View of a natural cast of the ventral valve, showing the muscular area and the 
diverging vascular sinuses, x 2. 
Figs. 49 to 54. Cyclospira uisulcata Emmons, sp 470 
49 and 50. Views from the dorsal and ventral valves of an ordinary specimen, x 2. 
51 and 52. Proflle and anterior views of the same specimen, x 2. 
53. Natural size view of the same specimen. 
54. A specimen fllled with crystalline calcite, preserving the sickle-shaped spiral 
bands and the connecting band, x 4. Collection of C. Schuchert. This draw- 
ing has the recurving portion of the primary lamellte entirely too divergent, 
while the loop should be more posteriorly or midway between the present 
position and the point of origin of the brachial supports. 
Figs. 55 to 58. Hallina saffordi W. and S 473 
55 and 56. Dorsal and ventral views of the type specimen. ^ 4. 
57 and 58. Dorsal and proflle views of the calcareous arm supports, x 4. Glade lime- 
stone, Lebanon, Tennessee. Collection of C. Schuchert. 
Figs. 59 to 64. Hallina nicolleti W. and S 474 
59 and 60. Two views of the common form of this species, x 4. 
61. Outline drawing to show the nature of the loop of the species. 
62 and 63. Opposite views of a large and more strongly plicated specimen, x 4. 
64. Outline proflle view of the preceding. Trenton limestone, Fountain, Minn. 
Collection of C. Schuchert. 
