1560 THE VOYAGE OF H.M.S. CHALLENGER. 



centre (the apex of the pyramid). Alternating with these, three horizontal, perradial, centrifugal 

 spines start from the base. 



Dimensions. Diameter of the basal triangle O'Ol, of the three meshes 0'005. 



Habitat. Fossil in different Tertiary deposits (of Sicily, Greece, North America); living in the 

 Central Pacific, Stations 270 to 272, depth 2600 to 2925 fathoms. 



5. Dictyocha tripyla, Ehrenberg. 



Dictyocha tripyla, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80. 

 Dictyocha tripyla, Ehrenberg, 1854, Mikrogeol., Taf. six. fig. 38 (et Taf. xxi.'fig. 41?). 



Each pileate piece of the skeleton is a small three-sided pyramid, similar to that of 

 Dictyocha triommata, but differs from it in the possession of three small perpendicular teeth, 

 which are directed downwards and start from the basal ring near the origin of the three horizontal 

 spines. 



Dimensions. Diameter of the triangular basal ring 0'015, of the three meshes 0'007. 



Habitat. Fossil in Tertiary deposits, North Africa (Oran), Sicily (Caltanisetta). 



6. Dictyocha medusa, n. sp. (PI. 101, figs. 13, 14). 



Each pileated piece of the skeleton has four equal, cruciate, triangular meshes. From the four 

 corners of the square basal ring proceed four perradial horizontal spines, and between these four 

 interradial curved bars, which correspond to the edges of a four-sided pyramid, arise from the 

 centre of the four sides and become united in the centre (on the apex of the pyramid). No apical 

 spine. 



Dimensions. Diameter of the basal ring 0'02, of the four meshes O'Ol. 



Habitat. Central area of the Pacific, Station 272, depth 2600 fathoms. 



7. Dictyocha staurodon, Ehrenberg. 



Dictyocha staurodon, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80. 

 Dictyocha staurodon, Ehrenberg, 1854, MikrogeoL, Taf. xviii. fig. 58. 



Each pileated piece of the skeleton is a small, regular, four-sided pyramid, similar to the fore- 

 going species. It differs from Dictyocha medusa in the development of a vertical apical spine, and 

 of four small centripetal teeth, which start from the inside of the basal square, between the four 

 perradial spines and the four ascending interradial beams. 



Dimensions. Diameter of the basal ring 0'025, of the meshes O'Ol. 



Habitat. Fossil in Tertiary rocks ; Tripel of Richmond, Virginia (Ehrenberg) ; Barbados, 

 (Haeckel) ; living in the Tropical Atlantic, Station 347, surface. 



