REPORT ON THE RADIOLARIA. 401 



polar tube (iu tig. 13 only on the upper pole), and so this species is transformed into Zygartus 

 chrysalis). 



Dimensions. — ^Length of the six-chambered inner cortical shell 0-25, of the middle 0-3, of the 

 outer 0-35; greatest breadth of the first 0-07, of the second Oil, of the thii'd 0-14; jjores (on an 

 average) 0-01 (0-002 to 0-02), bars 0-002 to O'OOS. 



Habitat. — Pacific, central area, Stations 272 to 274, depth 2350 to 2750 fathoms. 



Genus 174. Zygartus,'^ Haeckel, 1881, Prodromus, p. 463. 



Definition. — Z y g a r t i d a with triple (or multiple) cortical shell and double 

 medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main 

 axis. 



The genus Zygartus differs from Zygocampe by the development of two hollow 

 fenestrated tubes, on the two opposite poles of the main axis. It exhibits therefore to 

 the latter the same relation that Desmartiis does to Desmocampe and Ommatartus to 

 OmmatocamjM ; it difiers from these by the multiplication of the cortical shell, which 

 is composed of at least three concentric envelopes. 



1. Zygartus doliolum, n. sp. 



Inner cortical shell composed of six (or more) kidney-shaped chambers, all nearly of the same 

 size and structure, every chamber with four to five transverse rows of irregular, roundish pores, twice 

 to four times as broad as the bars ; the basal pores scarcely larger than the apical pores. Middle 

 cortical shell nearly of the same structure as the inner, only the pores larger and the bars thinner. 

 Outer cortical shell cylindrical, hemispherical at both poles, its network very delicate, with large 

 irregular, polygonal pores, and very thin bars between them; its surface covered with thin bristle- 

 like spines. Both medullary shells lenticular. Polar tube cylindrical, with conical apex, and with 

 very small pores; its length equals the breadth of two internal chambers, its breadth that of the 

 inner medullary shell. (This species appears to be a further developed form of Ommatocampe 

 annulata and Desmartus larvalis, PI. 40, fig. 12.) 



Dimensions. — Length of the six-chambered inner cortical shell 0-25, of the middle 0-3, of the 

 outer 0-35; greatest breadth of the first 0-07, of the second O'll, of the third 0-15; pores of the 

 inner shell 0-005 to 0-01, of the middle 0-003 to 0-007, of the outer 0-008 to 0-02; bars of the 

 fii-st 0002, of the second and third 0001; length of the polar tubes 0-15, basal thickness 0-02. 



Habitat. — Pacific, central area, Station 270, depth 2925 fathoms. 



2. Zygartus chrysalis, n. .sp. (PL 40, fig. 13). 



Inner cortical shell composed of six to twenty (commonly eight to twelve) chambers of different 

 size and form. Both proximal chambers nearly hemispherical, with spiny surface and subregular, 



^ Zyrjartus = hoaiv;\\h paired joints; £,v/6u, a'»Tof. 

 (ZOOL. CHALL. EXP. — PART XL.— 1885.) Rr 51 



