PLATE XV. 



1, 2. Astropyga sp. 



Fig. 1. Abactinal system of young Astropyga 13 mm. in diameter. 

 Fig. 2. Actinostoiue of same. 



3-19. Phormosoma placenta Wit. Thoms. 



Fig. 3. Young Phormosoma 8 mm. in diameter, showing the abactinal system, and a part of the ti t. 

 Fig. 4. Somewhat younger specimen 8 mm. in diameter, seen from the actinal Bide, showing the 

 sphasridia, suckers, and pedicellariee of that side of the test. 

 Somewhat older Phormosoma 17 mm. in diameter, seen from the abactinal side of the test. 

 The same, seen from the actinal side. 



Older specimen 20 nun. in diameter, seen from the actinal side. 

 The same seen from the abactinal side. 



Older specimen 28 mm. in diameter, seen from the abactinal side. 

 The same, seen from the actinal side. 



1 nun. in diameter, seen from the abactinal side. 

 The same, seen from the actinal side. 



i of anal system of young Phormosoma, 22 nun. in diameter, showing the mode of 

 deposition "f the limestone meshes forming the anal plates. 



Figs. 14-10 show tin ; mere accumulations of li cells, as in Fig. 14, which 



indicate tin- first position of the future tubercles, to Figs. 16, 15, IT, 18, and 1!), in which 

 the i i ibi iu mammary boss, and the perforation of the future tubercles are 



little by little indicated, 



