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



bars ; six to seven in the semicircle of one inner cupola, ten to twelve in the semicircle of one 

 outer cupola. Both shells are connected by eight radial beams, crossed in two diagonal planes. 



Dimensions. — Major axis of the outer shell O'l, minor 0'065 ; major axis of the inner shell 

 0-05, minor 0-04 ; pores 0-006, bars 0-002. 



Hahitat. — Western Tropical Pacific, Station 225, depth 4475 fathoms. 



Genu.s 291. Amphitholus,^ n. gen. 



Definition. — Tholonida -with simple cortical shell (-without external veil), -with 

 two hemispherical cupolas, opposite on the poles of one axis ; central chamber (bet-ween 

 them) Larnacilla-shaiped, v,-itb. medullary shell. 



The genus Amphitholus is the most simj^le form of all Coccotholida (or all 

 Tholonida pro-vided -wdth medullary shell). Its simple cortical shell exhibits, like 

 Tholartiis, tw^o lateral hemispherical cupolas, attached on both sides of a leutelleptical 

 central chamber (on the poles of its transverse axis). The central chamber has the 

 form of a triaxial ellipsoid, and contains, like Larnacilla, a small medullary shell, 

 connected -with it by the -wings of a latticed transverse girdle. Amphitholus may be 

 derived either from Tholartiis by secondary production of a cortical shell, or (more 

 probably) from Larnacilla by apposition of t-wo lateral dome-shaped protuberances. In 

 the latter case it may be regarded as an Amphipyle, the lateral open -^dugs of -n^hich are 

 closed by lattice--work. 



Subgenus 1. Amphitholissa, Haeckel. 

 Definition. — Surface of the shell smooth or rough, -without radial spines. 



1. Amphitliolus artiscus, n. sp. (PI. 10, fig. 3). 



Central chamber of the same height as both cupolas. Surface of the cortical shell rough. 

 Pores regular, circular, with prominent hexagonal frames, twice as broad as the bars ; eight to ten 

 in tlie basal semicircle of one cupola. 



Dimensions. — Major axis of the shell 0-16, minor axis O'l ; pores O'OOS, bars 0-004. 



Habitat. — Pacific, central area. Station 272, depth 2600 fathoms. 



2. Amphitholus artidium, n. sp. 



Central chamber one-fourth higher than both cupolas. Surface of the cortical shell smooth. 

 Pores irregular, roundish, once to three times as broad as the bars. (Very similar to Tholartus 

 tricolus, PI. 10, fig. 1, liut different l\y the medullary shell.) 



Dimensions. — Major axis of the shell 0-15, minor axis 0-12 ; pores 0-004 to 0-01, bars O'OOS. 



Habitat. — North Pacific, Station 241, depth 2300 fathoms. 



' Ampldtholus=&h.e\\ with two opposite cupolas; a^ip/, Siho;. 



