May, 1909. 



New Echinoids — Slocom. 



Petaloid Ambulacra: In some genera the ambulacral areas are wide 

 near the apex and the poriferous zones are bounded by a groove. The 

 part of the area having this form is called the petal (p). In other 

 genera the poriferous zones are similar in form to the above, but the 

 petals are not closed at their distal ends and the zones continue. The 

 disposition of the pores is, however, radically changed. Areas having 

 this form are called subpetaloid. 



Apical System (a) : A disc ordinarily composed of ten plates, (PI. II 

 fig. 5) five of which called genital plates form the summits of the inter- 

 ambulacral areas and five called radial plates, by some authors oculars, 

 form the summits of the ambulacral areas. Two or more of the 

 genital plates may be fused, thus reducing the number. One of the 

 genital plates is usually larger than the others and bears a spongy 

 protuberance filled with minute pores called the madreporite. 



b *~ pk 



Fig. 2. Diagram of the floscelle of Cassidulus intermedins. 



Floscelle: (Fig. 2) In the family Cassidulidae the ambulacral areas 

 assume a peculiar flowerlike form around the peristome, called the 

 floscelle. The floscelle is composed of five enlargements of the pori- 

 ferous zones called the phyllodes (ph). These five phyllodes are 

 separated from each other by five inflated plates of the interambulacral 

 areas about the peristomal margin. These inflated plates are called 

 bourrelets (b). 



Fascioles: Narrow bands apparently smooth but in reality formed 

 of microscopic tubercles, which during life bear vibrating cilia. They 

 have been divided into: (1) the peripetalous fasciole (pf) which sur- 

 rounds the petals; (2) the marginal fasciole which follows the sides; 

 (3) the subanal fasciole which is limited to the posterior face; and (4) 



