CONTENTS xiii 



PAGE 



Introduction . . 317 



A. The Apical System (Calyx) . 319 



1. echinoidea . 319 



2. astekoidea . . . 326 



3. Ophiiteoidea . 327 



4. Pelmatozoa 328 

 (a) Ceinoidea . 328 

 (6) Blastoidea . . 330 

 (c) Ctstidea . . .332 



B. The Oeal System of Plates . . 333 



C. The Perisomatio Skeleton . . 337 



1. Holothueioidea ... . 337 



2. eohinoidea . ..... 338 



(a) The Numeee of the Vertical Rows of Pla'jes . 339 



(6) The Poees of the Ameulaceal System . 340 



(c) The Symmetey of the Eohinoid Shell 340 

 {d) The Relation of the Ambulaoral and Inteeameu- 



laceal Plates to the Peristome . . . 344 

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



^ NEOTED ... ... 345 



(/) Special Modifications of the Ambulacra 346 



{g) Special Modifications of the Inteeeadii . . 348 



(A) FOEM OF THE Peeistome . 349 



(i) Oenamentation . . 349 



{k) Maeginal Incisions oe Peeforations . 349 



{I) The Perignathio Apophysial Girdle 350 



3. Asteeoidea ... . . 351 

 (a) The Ambulackal Skeleton . 351 

 (6) The Inteeambulacral Skeleton . 353 

 (c) The Accessory Skeletal System . . 354 

 {d) Comparison of the Perisomatic Skeleton of the 



Asteeoidea with that of the Echinoidea . . 355 



4. Ophiueoidea . ... . 355 

 (a) Skeleton of the Aems . 355 

 (J) The Oeal Skeleton . . . 358 



5. Ceinoidea . . 362 



(a) The Peeisomatic Skeleton of the Calyx . 362 



a. The Apical Capsule or Dorsal Cup 367 



i. The Tegmen Caly'cis . . 369 



(b) 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 



