PLATE 13. 
1-4. Porocidaris Cobosi A. Ag.; Station 3404. 
1, Showing the modification of the miliaries of an odd posterior interambulacral plate 
from the attachment of the muscles of the base of the spine in specimen measuring 
35 mm. in diameter. 
& 
Primary tubercle of the sixth interambulacral plate from the actinostome, the same 
specimen as fig. 1. 
? 
Last interambulacral plate of the left anterior interambulacrum, showing the piling up 
of the calcareous tissue to form the primary tubercle; the more solid perforated part 
& 
may be the mammelon. 
Shows the mode of growth of the calcareous tissue of the test laid up in strata, 
with the thin calcareous threads extending to the abactinal system, exterior view. 
> 
5. Dorocidaris papillata A. Ag. 
Abactinal system of young specimen 2.8 mm. in diameter, dredged off Key West in 
1388 fms. 
6. Goniocidaris canaliculata A. Ag. i 
Part of abactinal system of young specimen measuring 1.5 mm, in diameter. “Challen- 
> 
ger,” Station 844, shows the five genital plates, one of which is the madreporic 
genital. 
