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 01, minor 0'065 ; major axis of the inner shell 

 0-05, minor 0'04 ; pores O'OOG, bars 0'002. 



Habitat. Western Tropical Pacific, Station 225, depth 4475 fathoms. 



Genus 291. Amphitholus, 1 n. gen. 



Definition. T holonida with simple cortical shell (without external veil), with 

 two hemispherical cupolas, opposite on the poles of one axis ; central chamber (between 

 them) Larnacilla-shaiped, with medullary shell. 



The genus Amphitholus is the most simple form of all Coccotholicla (or all 

 Tholonida provided with medullary shell). Its simple cortical shell exhibits, like 

 Tholartus, two lateral hemispherical cupolas, attached on both sides of a lentelleptical 

 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 Tholartus by secondary production of a cortical shell, or (more 

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

 the latter case it may be regarded as an Amphipyle, the lateral open wings of which are 

 closed by lattice-work. 



Subgenus 1. Amphitholissa, Haeckel. 

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



1. Amphitholus 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 the basal semicircle of one cupola. 



Dimensions. Major axis of the shell 016, minor axis 01 ; 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 



, PI. 10, fig. 1, but different by the medullary shell.) 



Dimensions. Major axis of the shell 015, minor axis 012 ; pores 0'004 to O'Ol, bars 0'003. 

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



1 AmpJiitholus= Shell with two opposite cupolas ; <*,?>/, 6<*.os. 



