REPORT ON THE RADIOLARIA. 633 



Genus 279. Monozonium} n. gen. 



Definition. — P y 1 o n i d a with simple, spherical or suhspherical, central chamber, 

 surrounded by one single (transverse) latticed girdle. 



The genus Monozonium is the most simple and primitive of all Pylonida, and may 

 be regarded as their common ancestral form ; it may probably l)e derived phylogeneti- 

 cally either dii'ectly from Cenosphcera or from LentelUpsis, either by apposition of two 

 imperfect lateral chambers, or by surrounding it with an ecj^uatorial latticed girdle. This 

 transverse girdle is composed of three parts, the central chamber and two lateral wings, 

 which represent two short hollow latticed tubes, the axes of which are parallel to the 

 principal axis. On both j^rincipal sides (on the anterior and posterior faces) there are two 

 large open gates as in Amphipyle. If we imagine the openings of the tube-shaped 

 lateral wings closed by lattice-work, Monozonium becomes transformed into Tliolartus, 

 the most simple form of Tholonida. Probably in all Pylonida the ontogeny of the shell 

 begins with the formation of a Monozonium. 



Subgenus 1. Monozonaris, Haeckel. 

 Definition. — Shell smooth or rough, without radial spines or thorns. 



1. Monozonium primordiale, n. sp. 



Central chamber of the shell spherical, smooth, with three to four pores on the half equator. 

 Both wings of the girdle of the same breadth, but of twice the length of the central chamber, with 

 three to four longitudinal rows of pores. No radial spines. 



Dimensions. — Diameter of the central chamber 0-02 ; breadth of the wings 0-02, length 0-04 ; 

 pores and bars 0-003. 



Eahitat. — Pacific, central area. Station 271, surface. 



2. Monozonium alatum, n. sp. (PI. 9, fig. 1). 



Central chamber of the shell lentelHptical, smooth, one and a half times as long as broad, with 

 three to four pores on the half equator. Both wings of the girdle twice as broad, and somewliat 

 longer than the central chamber, with five to si.x longitudinal rows of pores. No radial spines. 



Dimensions. — Length of the central chamber 0-03, breadth 0-02 ; breadth of the wings 0-04, 

 length 0-05 ; pores and bars 0'004. 



Habitat. — North Pacific, Station 241, surface. 



1 Monozonium = "With one girdle ; ftoui^aviou. 



(ZOOL. CHALI.. EXP. — PART XL. — 1885.) Er 80 



