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



Fig. 2. Same, seen in profile. 



,, 3. Magnified portion of the posterior extremity, denuded, seen in profile. 

 ,, 4. Anal snout, seen from the actinal side, denuded. 

 ,, 5. Anal snout, seen from the abactinal side, covered wdth spines. 

 „ 6. Anal extremity, showing snout, and the connection of intestine with anal system. 

 ,, 7. End view of the anal snout. 



,, 8. Actinal groove and portion of actinal surface surrounding it, covered with spines. 

 ,, 9. Interior view of actinostome, with adjoining plates, forming the actinal groove. 



,, 10. Actinal edge of actinal groove, showing the plates adjoining it. 



,, 11. Profile of actinal groove, seen from the interior. 



,, 12. Abactinal system denuded. 



,, 13. Interior view of abactinal part of test, with genital organs. 



,, 14. Interior view of apical part of lateral anterior ambulacra. 



,, 15. Large primary spines of the rounded keel, forming edges of anterior part of test. 



PLATE XXIX. 



Urechinus naresianus, A. Ag. (figs. 1-4), p. 146. 



Fis;. 1. Seen from the abactinal side of the test. 



2. Same, seen in profile. 



3. Same, seen from the actinal side. 



4. Same, seen facing the anal extremity. 



Cystechinus tvi/villii, A. Ag. (figs. 5-8), p. 152. 



5. Seen in profile. 



6. Same, seen facing the odd anterior ambulacrum. 



7. Same, seen from the abactinal side. 



8. Same, seen from the actinal side. 

 All figures natural size. 



PLATE XXIX*. 



Cystechinus wyviUii, A. Ag. (figs. 1-20), p. 152. 



Fig. 1. Young specimen, measuring 16 mm., seen from the abactinal side. 



,, 2. Same, seen from the anal extremity. 



„ 3. Same, seen from the actinal side. 



,, 4. Same, seen in profile. 



'■o' 



