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



The genus Acrosphcera differs from its ancestral genus CoUosjyhcera by the 

 development of spines on the outer surface of the shell. These are either short, 

 straight, radial spines, or oblique and often curved ; theii' base is often inflated ; they 

 are irregularly scattered on the whole surface between the pores. 



1. Acrosphcera erinacea, n. s]). 



Shell a regular sj)here, everywhere covered with small, very numerous, straight radial spines, 

 regularly scattered between the pores. In the half meridian of the shell ten to twelve circular 

 pores, all of the same form and size, double as broad as the bars. Spines bristle-shaped, very thin, 

 solid, about as long as the diameter of the pores. 



Biincnsions. — Diameter of the shell O'l to 0'12, of the pores O'OOS to 0"012 ; length of the 

 spines O'Ol. 



Habitat. — Tropical zone of the Atlantic, coast of Brazil, Eabbe, surface. 



2. Acrosphcera echinoides, n. sp. (PI. 8, fig. 1). 



Shell a regular sphere, covered with nxunerous, straight, radial spines, irregularly scattered over 

 the whole surface. In the half meridian of the shell twenty to thirty irregular roundish pores of 

 variable size, one to four times as broad as the bars. Spines conical, strong, quite radial, at the top 

 of small conical elevations, which are perforated by from three to six pores. 



Dimensions.- — Diameter of the shell 012 to 015, of the pores 0-002 to O'OOS ; length of the 

 spines 0'015, of their basal zones O'Ol. 



Hahitat. — South-east corner of the Pacific, Valparaiso, Station 298, surface. 



3. Acrosphcera setosa, Haeckel. 



Polysolenia setosa, Ehrenberg, 1872, Abhandl. d. k. Akad. d. "Wiss. Berlin, p. 299, Taf. viii. 

 fig. 10. 



Shell a regidar sphere, covered with niuneroiis bristle-shaped radial spines, irregularly scattered 

 between the pores. In the half meridian of the shell two to four very large circular pores (equal 

 to one-third the radius), and between them numerous very small, point-like pores. ^ 



Dimensions. — Diameter of the shell 0'05 to 0'08, of the large pores O'Ol, of the small O^OOl ; 

 length of the spmes 01 to 0-02 



Habitat. — West Tropical Pacific, Phihppine Sea, Station 206, depth 2100 fathoms. 



4. Acrosphcera spinosa, Haeckel. 



Collosphcera spinosa, Haeckel, 1862, Monogr. d. EadioL, p. 536, Taf. xxxiv. figs. 12, 13. 

 Collosphcera spinosa, Cieakowsky, 1871, Arcliiv f. mikrosk. Anat., vii. p. 374, Taf. xxix. 

 figs. 7-17. 



SheU a regular or subregidar sphere, covered with numerous, obliquely standing spmes, irregu- 

 larly scattered over the surface. In the half meridian of the shell fifteen to twenty irregular 



