xvi CONTENTS 



Page 

 4. Development of some Silurian Beachiopoda — Con- 

 tinued 



General Form and Outline 368 



Beak and Foramen 369 



Atrypina disparilis Hall, 1852 369 



Specific Characters 370 



Mature Form 370 



Variations in Outline 370 



Abnormalities 370 



Developmental Changes 371 



Meristina rectirostris Hall, 1882 372 



Specific Characters 373 



Mature Form 373 



Incipient Form 373 



Developmental Variations . . 374 



General Form and Outline 374 



Beak 374 



Foramen 374 



WUtfieldella nilida Hall, 1843 374 



Specific Characters 375 



Mature Form 375 



Variations in Outline 375 



Incipient Form 376 



Developmental Variations 376 



Meristina Maria Hall, 1863 377 



Specific Characters . 378 



Mature Form 378 



Incipient Form 379 



Developmental Variations . ...... 379 



General Form and Outline 379 



Beak 379 



Foramen 379 



Spirifer crispus Hisinger, 1826 380 



Spirifer crispuSjyar. simplex HaW, 1879 .... 380 

 Reticularia fti'costafa Vanuxem, 1842, var. petila Hall, 



1879 380 



Spirifer radiatus Sowerby, 1825 382 



Incipient Form 382 



Developmental Changes 383 



Summary of Developmental Changes 386 



Size and Contour . 886 



Valves 388 



Beaks 889 



Cardinal Area 389 



Internal Apparatus 395 



Surface Ornaments ......... 396 



Varieties and Abnormalities 397 



