I 



i 



Plati-: 13. 

 1-4. Porocidaris Cobosi A. Ag. ; Station 3404. 



1. Showing the modiiicution 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. 



2. Primary tubercle of the sixth interambulacral plate from the actinostome, the same 



specimen as fig. 1. 



3. 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. 



4. 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. 



5. Abactinal system of young specimen 2.8 mm. in diameter, dredged off Key West ia 



138 fms. 



6. Goniocidaris canaliculata A. Ag. 



G. Part of abactinal system of young specimen measuring 1.5 mm, in diameter. "Challen- 

 ger,'" Station 844, sliows the five genital plates, one of which is the madreporic 

 genital. 



