LIST OF FIGURES IN TEXT. 



Pholidops oblata Hall. Nepionic ami early ncanic stages . . 85 



" " " X'entral valve . . . . . .86 



" " " Dorsal valve . . . . . .86 



T7-ematis viillepitncta W7\\\. Interior of dorsal valve . . .86 



StropJieodonhi incrqitis/riafa. \'entral muscle area and ridges . . 89 



" " Area in \entral valve . . .89 



" " Interior of the dorsal valve . . .89 



'" " " " " " " adult . . 89 



" pc'rplatia Conrad. Dorsal valve showing shell in 



nepionic stage, fold and origin of striae . . 92 



" perplana. Outline of ventral valve, showing acumi- 



nate cardinal extremities . . . . .92 



" poplaiia. Interior of ventral valve . . . .92 



PltolidostropJiia iowa'inisis. Ventral \'alve, showing acuminate car- 

 dinal extremities . . . .96 



" " Interior of ventral valve, showing adduc- 



tor and diductor muscle scars . 96 



" " Interior of dorsal valve . . .96 



StropheOihvita concava Hall. Sketch of cardinal process and muscle 



area . . . . . -99 



" jimia Hall. Part of the muscle area of ventral valve 99 



OrtJiothctt's cJicmioigensis Conrad. Specimen retaining both valves 102 

 " " Ventral view . . . .102 



" " Cardinal view 



" arctist7'iatiis\\?A\. Diagram of dorsal valve 103 



" pectenacea " Dorsal valve 



" Diagram showing inception of plications 



Clionetes coronaius (Conrad). Dorsal valve, young specimen . 

 scitultts Hall. \'entral and dorsal valves . 

 robustus Raymond. Ventral valve .... 



Stropkolosia frttncata Hall. Dorsal beak .... 



Rhipidomella vaiiuxciiii Hall. Ventral \alve .... 



Ti-opidoleptus carinatiis Conrad. Series showing change in relative 



convexity of valves 

 Trigcria lepida Hall. Series showing growth .... 



EunellalinckliPni " Young specimen with open delthyrium. 



103 

 104 

 109 



113 

 118 

 122 

 124 



127 

 133 

 134 

 134 



