Figs. 1 to 8. 

 1 and 2. 

 3 and 4. 



5,6 and 7. 



Figs. 9 to 25. 

 9, 10 and 11. 



12. 



13 and 14. 

 15, 16 and 17. 



18 and 19. 

 20,21, 22 and 23. 



24. 

 25. 



Figs. 26 to 29. 

 26 and 27. 



28 and 29. 



Figs. 30 to 34. 



30, 31 and 32. 



33. 



34. 

 Figs. 35 to 37. 



Figs. 38 to 41. 

 38, 39 and 40. 



41. 



Figs. 42 to 44. 

 42, 43 and 44. 



Figs. 45 to 48. 



45 and 46. 



47. 



48. 



Figs. 49 to 54. 

 49 and 50. 

 51 and 52. 



53. 



54. 



Figs. 55 to 58. 

 55 and 56. 

 57 and 58. 



Figs. 59 to 64. 

 59 and 60. 



61. 

 62 and 63. 



64. 



PLATE XXXIV. 



PAGE. 

 EHYNCIIOTKEMA AINSLIEI N. H. Winchell ........................................ 459 



Views of the dorsal and ventral valves of a typical example. 



Profile and anterior views of the same specimen. Near Lanesboro, Minn. Min- 



nesota Geological Survey collection. 



Dorsal, ventral and profile viws respectively of an immature specimen, x 2. 

 The same specimen, natural size. Trenton shales, Minneapolis, Minn. Minne- 

 sota Geological Survey collection. 



459 



RHYNCIIOTREMA iN^EQUivALVis Castclnau ...................................... 



Dorsal, ventral and profile views respectively of a specimen from the Trenton 



limestone and approaching B. orientalis Billings, x 2. 

 A view from the dorsal valve of a strongly lamellose variety of this species 



occurring in the Clitambonites beds, x 2, St. Paul, Minn. 

 Ventral and profile views of the same specimen, natural size. 

 Three views, a ventral, dorsal and profile respectively, of another variety found 



in the middle third of the Trenton shales. Collection of C. Schuchert. 

 Two views, ventral and profile, of a thin immature specimen. Fountain, Minn. 

 Dorsal, ventral, profile and anterior views respectively of a large but typical 



specimen of this species. Trenton shales, Minneapolis, Minn. Minnesota 



Geological Survey collection. 



An interior view of the ventral valve showing the muscular scars and teeth, x 2. 

 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. 



R. INJEQUIVALVIS var. LATICOSTATA W. and S .................................... 461 



Dorsal and ventral views of a very characteristic specimen showing the prom- 



inent lateral costae. 

 Profile 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. 



RHYNCHOTREMA CAPAX Conrad, sp .................. ............................ 462 



Three views of a large matured specimen. 



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. 

 The interior of a very thick ventral valve. Hudson River group, Iron Ridge, 



Wisconsin. Minnesota Geological Survey collection. 



RHYNCHONELLA ? NEENAH Whitfleld ........................................... 465 



Dorsal, anterior and profile views of the type specimen. 

 Hudson River group, Delafleld, Wisconsin. 



(After Whitfleld.) 



ZYGOSFIRA RECURVIROSTRA Hall, Sp 466 



Three views of a typical example of this species, x 2. Galena shales near 

 Cannon Falls, Minn. Minnesota Geological Survey collection. 



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 lamellae, x 4. Collection 

 of C. Schuchert. 



ZYGOSPIRA MODESTA (Say Ms. ) Hall 467 



Dorsal, ventral and profile 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. 



ZYGOSPIRA UPHAMI W. and S 468 



Ventral and profile views of a typical example. 

 View from the dorsal valve of the same specimen, x 2. 



View of a natural cast of the ventral valve, showing the muscular area and the 

 diverging vascular sinuses, x 2. 



CYCLOSPIRA HISULCATA Emmons, sp 470 



Views from the dorsal and ventral valves of an ordinary specimen, x 2. 



Profile and anterior views of the same specimen, x 2. 



Natural size view of the same specimen. 



A specimen filled 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 lamellae 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. 



x 4. Glade lime- 



HALLINA SAFFORDI W. and S 



Dorsal and ventral views of the type specimen, x 4. 

 Dorsal and profile views of the calcareous arm supports, 

 stone, Lebanon, Tennessee. Collection of C. Schuchert. 



HALLINA NICOLLETI W. and S 



Two views of the common form of this species, x 4. 

 Outline drawing to show the nature of the loop of the species. 

 Opposite views of a large and more strongly plicated specimen, x 4. 

 Outline profile view of the preceding. Trenton limestone, Fountain, Minn. 

 Collection of C. Schuchert. 



473 



474 



