PAGE. 



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 (DlNORTHIS) SUBQUADRATA Hall 428 



46, 47 and 48. Dorsal, ventral and profile views 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 Eiver group, Spring Valley, Minn. 



50. Interior of a dorsal valve. (After Meek, Ohio Pal., vol. i.) 



Figs. 51 to 58. ORTHIS (DINORTHIS) PROAVITA 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 River 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. RAFINESQTIINA 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. 



