298 THE VOYAGE OF H.M.S. CHALLENGER. 



Fig. 11. Same, seen facing the anterior extremity. 

 All figures natural size. 



PLATE XXVJa. 



Spatagocystis challengeri, A. Ag. (figs. 1-17), p. 141. 



Fig. 1. Interior view, slio-^vdng course of alimentary canal, seen from the actinal side. 

 „ 2. Portion of test showing the arrangement of the plates surrounding the right 



anterior part of the actinal surface, magnified. 

 ,, 3. Magnified view of actinal groove, covered with spines. 

 ,, 4. Actinal view of part of the test, showing the arrangement of the plates along the 



median part of the actinal surface, and posterior part of the actinal groove. 

 ,, 5. Interior view of the pouch forming the anal system. 

 „ 6. Interior profile view of pouch, and termination of intestine in the posterior end 



of the pouch. 

 „ 7. Abactinal view of anal snout ; test projecting over this removed. 

 ,, 8. Magnified view of abactinal system and surrounding plates. 

 ,, 9. Interior view of apical part of lateral anterior and posterior ambulacra, and the 



enclosed lateral interambulacrum and adjoining ambulacrum. 

 ,, 10. Interior view of part of the abactinal median ridge (the pores should be in the 



outer plates) ; the median rows of plates are the interambulacral plates. See 



fig. 17. 

 „ 11. Interior view of the posterior part of the actinal surface, showing the course of 



the lateral posterior ambulacra, and arrangement of the plates forming the 



base of the anal snout. 

 ,, 12. Same, seen from the actinal side, showing the large tuberculatiou forming the 



keel of the actinal plastron. 

 ,, 13. Profile view of anal snout. 

 ,, 14. Exterior view of part of test of anterior lateral ambulacra and adjoining inter- 



amlDulaera, showing the uniformity of the tuberculatiou. 

 „ 15, 16. Two views of the posterior extremity of test, seen in profile, one shaded to 



show the tuberculatiou, the other to show the arrangement of the plates and 



course of the aml:)ulacral pores. 

 ,, 17. Posterior extremity of the test, seen from the abactinal side, showing the 



arrangement of the plates and course of the lateral posterior ambulacra! tubes. 

 Fig. 1, natural size ; aU others somewhat magnified. 



