PLATB UV— CoDUnneit. 



SuBOKNus CATAZYGA, s.-oen. nov. 



Pnge.l.'iT. 



C'atazyga IIeadi, liillings. 



Figs 24-36. Dorsal, nrotile aiul cardinal views of the exterior ; allowing the biconvex valves, the tine plica- 

 tion of the exterior and the median depression on the brachial valve. Natural size. 



Hudson River group. Near Ottawa, Canada. 

 Figa. S8, 39. Dorsal and proBle views of another specimen. 



Hudson River group. Near Cincinnati, Ohio. 

 Vig. 80. The interior of a jwrtion of the pedicle-valve ; showing the deep muscular scar. 



Hudson River group. WayntitviUe, Indiana. 



Catazyoa Headi, viir. bokealis, Billings. 

 Fig. 87. A dorsal view of a rather large sjiecimen of this variety. 



Hudson River group. Waynesville, Indiana. 

 Figa. 81, 82. Dorsal and profile views of a smaller shell. 



Anticosti group. Island of Anticosti. 



Catazyoa Headi, var. Anticostiensis, Billings. 



Fig. 83, 84. Ventral and dorsal views of the exterior; showing the outline, contour and tine surface 

 plication. 



Hudson River group. CoUingiDood, Ontario. 



Genus ZYGOSPIRA, Hall. 



Page 151. 



Zygosi'ira putilla, sp. nov. 

 Figs. 86-37. Dorsal, profile and ventral views of the exterior of an average example. X 2. 

 Hudson River group. Near Edgewood, Pike county, Missouri. 



Genus CYCLOSPIRA, gen. nov. 



Page 146. 



Cyclosi'ira bisulcata, Emmons. 



Figs. 38-40. Dorsal, profile and ventral views of the exterior of a specimen bearing a marginal plication in 

 the sinus of the brachial valve. X 2. 



Trenton limestone. Watertovm, N. T. 



Genus DAYIA, Davidson. 



Page 62. 



Dayia navicula, Sowerby. 

 Figs. 41-43. Dorsal, frontal and profile views of an average example, enlarged. 

 Fig. 44. A restoration showing the character of the spirals and loop. 



Figs. 45, 46. Enlarged translucent preparations of the spirals ; showing the lateral direction of the apices 

 and the fimiji-iation of the 8|>iral coils. (Davidsok.) 



Ludlow shales. Shropshire, England. 



Genus PROTOZYGA, gen. nov. 



Page 151. 



Protozyga exioua, Hall. 



Figs. 47, 48. Ventral ami dorsal views of a specimen ( showing the naviculate contour and smooth exterior. 

 Shells of this S)>ecies usually bear one or two low, broad marginal folds on each side of the 

 metlian axis. X 2. 



Trenton limestcme. IVatertown, N. Y. 



