CONTENTS xiii 



PAGE 



iNTEODrCTION ....... 317 



A. The Apical System (Calyx) ..... 319 



1. echinoidea ....... 319 



'2. asteroidea ....... 326 



3. Ophiukoidea ....... 327 



4. Pelmatozoa ....... 328 



(«) Crinoidea ....... 328 



(b) Blastoidea ....... 330 



(c) Cystidea ....... 332 



B. The Oral System of Plates ..... 333 



C. The Perisomatic Skeleton ..... 337 



1. Holothurioidea ...... 337 



2. Echinoidea ....... 338 



(«) The Number of the Vertical Rows of Plates . 339 



(&) The Pores of the Ambulacral System . . 340 



(c) The Symmetry of the Echinoid Shell . . 340 



(d) The Relation of the Ambulacral and Interambu- 



lacral Plates to the Peristome . . . 344 



(e) Manner in which the Skeletal Plates are Con- 



nected ....... 345 



(/) Special Modifications of the Ambulacra . . 346 



(g) Special Modifications of the Interradii . . 348 



(A) Form of the Peristome ..... 349 



(t) Ornamentation ...... 349 



{k) Marginal Incisions or Perforations . . . 349 



{I) The Perignathic Apophysial Girdle . . . 350 



3. Asteroidea ....... 351 



(a) The Ambulacral Skeleton .... 351 



{b) The Interambulacral Skeleton . . . 353 



(f) The Accessory Skeletal System . . . 354 

 {d) Comparison of the Perisomatic Skeleton of the 



Asteroidea with that of the Echinoidea . . 355 



4. qphiuroidea ....... 355 



(a) Skeleton of the Arms ..... 355 



(b) The Oral Skeleton ..... 358 



5. Crinoidea ....... 362 



(«) The Perisomatic Skeleton of the Calyx . . 362 



a. The Apical Capsule or Dorsal Cup . 367 



b. The Tegmen Caly'cis . . . . .369 

 (6) The Brachial Skeleton ..... 370 



(c) The Stem (Columna) ..... 373 



(d) The Manner of Connection between the Skeletal 



Pieces ....... 376 



(e) The Nerve Canals of the Arms and of the Apical 



Capsule ....... 377 



