238 THE FOEAMINIFEEA 



Huh-fainilij 3. Nummulitin.e. 



Test lenticular or complanate ; lower forms with 

 thickened and finely tubulated shell-wall, but no 

 intermediate skeleton ; higher forms with supple- 

 mental skeleton and complex canal system. 



Genus ArcJuEdiscus, Beady. 



Test lenticular, consisting of a non-septate tube 

 coiled upon itself in constantly varying direction, 

 embedded in a thick mass of finely tubulated shell- 

 substance. No supplemental skeleton nor canal 

 system. Cm-boniferous. 



Example. — A. Karreri, Brady, 'Ann. Mag. Nat. 

 Hist.' ser. 4, vol. xii. 1873, p. 286, pi. xi. ; ' Monogr. 

 Carb. and Perm. Foram.' (Pal. Soc), 1876, p. 142, 

 pi. xi. figs. 1-6. 



The only species of this remarkable genus is of a 

 lenticular rounded form, with a somewhat angular 

 margin. The aperture is situated at the open end of 

 the tubular cavity, in various positions on the peri- 

 phery, according to the development of the shell ; 

 rounded or crescentic, and simple. The presence of 

 the coarser pores in this shell probably points to the 

 early stage of a canal system, which is, however, 

 obscured by the mineralisation of the fossils. It 

 appears to be restricted to the Carboniferous forma- 

 tions of the British Islands. (Plate 13, figs. F, /.) 



