60 



THE VOYAGE OF H.M.S. CHALLENGER. 



different cases of regular disposition were observed : — (A) two opposite beams in one 

 axis ; (B) four beams, opposite in pairs in two axes perpendicular one to another ; (C) 

 six beams, ojiposite in pairs in the three dimensive axes ; (D) eight beams, opposite in 

 pairs in the four diagonals of the regular cube ; (E) twelve beams corresjjonding to 

 the twelve axes of the regular icosahedrou ; (F) fourteen beams quite regularly disposed 

 (six corresponding to the three axes of the regular octahedron, eight to the central points 

 of its faces) ; (Gr) twenty beams (probably corresponding to the twenty corners of a 

 regular dodecahedron) ; (H) thirty -two beams, regularly disposed. Earely the number of 

 the radial beams is intermediate between these eight cases, and rarely it is higher ; 

 then commonly the disposition is irregular. The regularity of their disposition in the 

 great majority of cases is very remarkable and evident. 



Synoi^sis of the Genera of Liosphcerida. 



\ Sliull-cavity simple, 



I. Subfamily 



EtlimosphseriJa. 

 (Shell one single latticed sphere.) 



IL Subfamily 



Carposphserida. 

 (Two concentric spheres. ) 



III. Subfamily 



Tliecosphaerida. 

 (Three concentric spheres.) 



IV. Subfamily 



Cromyospliwrida. 

 (Four concentric spheres. ) 



Y. Subfamily . 



Caryosphaerida. 

 (Five or more concentric spheres. ) 



VI. Subfamily 



PlegmosphreriJa. 

 (Spherical sliell wholly or partially of 

 spongy structnre. ) 



Pores of the shell simple, 



not prolonged into free \ Shell-cavity withradial 

 tubuli. I beams uuited in the 



[ centre, 



[ Tubuli external, centri- 

 Pores prolonged iuto free | fugal, 

 conical or cylindrical \ 

 tubuli. I Tubuli internal, centri- 



[ petal, 



f One shell medullary (intracapsular), the other 



\ 



cortical (e.\t.racapsular), 



[ Both shells cortical (near together). 



f Two shells medullary (intracapsular), one shell 

 I cortical (extracapsular), 



I One shell medullary (intracapsular), two shells 

 [ cortical (extracapsular), 



I Two inner medullary shells (intracapsular), and two 

 j outer cortical shells (extracapsular), 



Two inner medullary shells, and three or more outer 

 cortical shells, ..... 



Spongy sphere 'without 

 latticed medullary 

 shell in the centre. 



Spongy sphere with one 

 or two latticed medul- 

 lary shells in the 

 centre. 



Sphere solid, . 



Sphere with a central 

 cavity. 



One single medullary 

 shell, 



Two concentric medul- 

 lary shells, 



1 5. Cenob~plicera. 



16. Stigmosphcera. 



17. Ethmosphmra. 



18. Sethusphara. 



19. Carposijlunra. 



20. LiosphcE^-a. 



21. Tlipcosphcera. 



22. Rhodospihoira. 



23. Cromyosphcera. 



24. Caryosjphcem. 



25. Styptosphwra. 



26. Plegmosphcera. 



27. Spongoplegma. 



28. Spongodidyon. 



