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



3. Acanthonia denticulata, n. sp. 



Spines quadrangular prismatic, with prominent elegantly denticulated edges, of equal breadth 

 throughout their whole length. Both ends pyramidal, without leaf-cross. (Similar to Amphilonche 

 denticulata, but with the twenty spines all equal, and with spherical central capsule.) 



Dimensions.- Length of the spines 012 to 016, breadth O'OOS. 



Habitat. Central Pacific, Stations 266 to 274, surface. 



4. Acanthonia mulleri, Haeckel. 



Acanthometra mulleri, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf. xv. fig. 3, Taf. xviii. fig. 6. 



Spines quadrangular, nearly prismatic, but tapering gradually from the pyramidal base towards 

 the distal bifid apex, which bears two thin, parallel, or little divergent teeth ; four edges elegantly 

 denticulated ; base without leaf-cross. Central capsule yellowish or reddish. 



Dimensions.- Length of the spines 012 to 018, basal breadth O'OOS. 



Habitat. Mediterranean (Messina) ; Atlantic, Stations 348 to 352, surface. 



5. Acanthonia fragilis, Haeckel. 



Acanthometra fragilis, Haeckel, 1862, Monogr. d. Eadiol., p. 380, Taf. xv. fig. 4, Taf. xviii. 

 fig. 7. 



Spines quadrangular, nearly prismatic, but gradually thickened from the pyramidal base 

 towards the distal truncated end ; four edges regularly denticulated ; base without leaf-cross. 

 Central capsule opaque. 



Dimensions. Length of the spines 0'5 and more, basal breadth 0'002 to 0'003, distal breadth 

 0-008 to 0-016 or more. 



Habitat. Mediterranean (Messina); North Atlantic, Station 354, surface. 



6. Acanthonia convexa, n. sp. 



Spines quadrangular, with four broad lamellar, convex, prominent edges, which from the 

 broader middle part are thinned towards the two emarginated ends ; each end with a small quadran- 

 gular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, 

 which is seen in the caudal or posterior (geotomical) spine of Amphilonche, anomala (Monogr. d. Eadiol., 

 Taf. xviii. fig. 23, b). 



Dimensions. Length of the spines 012 to 016, breadth in the middle part 0'02 to 0'025. 



Habitat. North Pacific, Station 244, surface. 



7. Acanthonia concava, n. sp. 



Spines quadrangular, with four broad lamellar, concave, prominent edges, which from the 

 smaller middle part are broadened towards the two emarginated ends ; each end with a small quadran- 



