PLATE XV. 
1, 2. Clypeaster Ravenellii A. Ao. 
Fig. 1. Seen from the abactinal side, natural size, partly denmled. 
Fig. 2. Part of one of the ambulacral zones of the actiual side, magnified. 
3, 4. Clypeaster latissimus A. Ao. 
Fig. 3. Seen from the abactinal side, natural size ; half the test denuded. 
Fig. 4. Part of one of the iuterambulacral zones of the abactinal side, magnified. 
