REPOET ON THE RADIOLARIA. 537 



regular (like Dictyastrum), partly bilateral (like Rhopcdastrum). If the number of 

 species increases much, these two subgenera may be separated into two genera : 

 Chitonastvella corresponding to the former, Chitonastromma to the latter. 



Subgenus 1. ChitonastreUa, Haeckel. 



Definition. — All three arms of the same size and form, equidistant ; fundamental 

 form of the shell therefore an equilateral triangle. 



1. Chitonastrum triglochin, n. sp. 



All three arms equal and equidistant. Each arm has the form of an isosceles triangle, twice 

 as high as broad ; the truncated apex of the triangle is inserted into the large central disk, 

 whilst its cHstal base (four times as broad) is divided by a deep incision (half as long as the arm). 

 Each arm with teu to twelve joints, simple in its basal half, double in its distal half. Axes 

 of the six branches straight. (Resembles Trigonastrum regularc, PI. 43, fig. 16, but differs in the 

 absence of a patagium.) 



Dimensions. — Eadius of each arm 0'24, greatest breadth 0"11, basal breadth 0'03. 



Habitat. — Pacific, central area, Station 271, depth 2425 fathoms. 



2. Chitonastrum hathyhium, n. sp. 



All three arms equal and equidistant, in the basal two-thirds simple, rectilinear, three times as 

 long as broad, in the distal third forked, both branches equal, straight, blunt, half as broad as the 

 basal part. 



Dimensions. — Eadius of each arm 0'18, basal breadth 0'04, breadth of the branches 0'02. 



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



Subgenus 2. Chitonastromma, Haeckel. 



Definition. — One odd arm different in size or form from the two other arms, 

 which are paired ; distance between them different ; fundamental form of the shell 

 therefore a bilateral, isosceles triangle. 



3. CJiitonastrum jugatum, n. sp. (PI. 43, fig. 14). 



Dictyastrum jugatiim, Haeckel, 1881, Prodromus et Atlas (pi xliii. fig. 14). 



Arms very different ; odd arm club-shaped, twice as long as broad, at the blunt distal end 

 twice as broad as at the base ; its axis is perpendicular to the common axis of both paired arms, 

 which are only two-thirds as long, not so broad, and in the distal half divided into two branches ; 

 the anterior branch is straight, nearly horizontal, the posterior shorter and curved backwards. 



(ZOOL. CHALL. EXP. — PART XL. — 1885.) Er 68 



