CONTENTS xv 



PAGE 



4. DEVELOPMENT OF SOME SILURIAN BRACHIOPODA Con- 

 tinued 



Developmental Variations 349 



General Form and Outline 349 



Beak 350 



Foramen 350 



Plications 351 



Rhynchotreta cuneata Dalinan, 1827, var. americana 



Hall, 1879 351 



Specific Characters 352 



Mature Form 352 



Incipient Form 353 



Developmental Changes 353 



Contour 353 



Fold and Sinus 353 



Beak 354 



Surface Ornaments 354 



Cardinal Area 355 



Variations 356 



Atrypa reticularis Linnaeus, 1767 356 



Specific Characters 356 



Mature Form 356 



Incipient Form .'......... 357 



Developmental Variations 358 



General Form and Outline 358 



Beak 358 



Foramen , . . . 358 



Plications 359 



Summary 359 



Homceospira evax Hall, 1863 360 



Specific Characters 360 



Mature Form 360 



Variations from the Normal Development . 361 



Developmental Variations 362 



Beaks 363 



Foramen 363 



Sinus 364 



Plications 364 



Internal Apparatus 364 



Homceospira sobrina sp. nov 366 



Specific Characters 367 



Mature Form 367 



Variations from the Normal Mature Form . 368 



Incipient Form 368 



Developmental Variations 368 



