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Figs. 43 to 45. O. (D.) meedsi, var. German A W. and S 428 
Dorsal, ventral and profile views of a very characteristic specimen of this variety. 
Galena shales, near Cannon Falls, Minn. Collection of C. Schuchert. 
Figs. 46 to 50. OrTHIS (DmORTHIS) SUBQUADRATA Hall — 428 
46, 47 and 48. Dorsal, ventral and profile vievFS respectively of an entire specimen. Minnesota 
Geological Survey collection. 
49. An interior view of the ventral valve of a very old specimen in which the anterior 
margin is much thickened and reflexed. The vascular sinuses are abnormally 
developed, due to old age. Hudson River group, Spring Valley, Minn. 
50. Interior of a dorsal valve. (After Meek, Ohio Pal., vol. i.) 
Figs. 51 to 58. Orthis (Dinorthis) proa vita W. and S 431 
51, 52 and 53. Dorsal, ventral and profile views of an entire specimen. Collection of the Min- 
nesota Geological Survey. 
54 and 55. Dorsal and profile views of a large specimen. Hudson Eiver group, Wilmington, 
Illinois. 
56 and 57. Interior and profile views of a thick ventral valve. Hudson River group, Spring 
Valley, Minn. 
58. Interior of a dorsal valve. Hudson River group. Spring Valley, Minn. Collec- 
tion of C. Schuchert. 
Figs. 59 and 60. Rafikesquina alternata, var. loxorhytis Meek 407 
59. Perpendicular view of the hinge and muscular impressions of the specimen illus- 
trated on plate XXXI, fig. 37. 
60. Profile view of the same specimen. 
