REPORT ON THE RADIOLARIA. 909 



1. Triplagia primordialis, n. sp. (PI. 91, fig. 2). 



Spines straight, of equal size and similar form, equidistant, three-sided prismatic, each with two 

 pairs of opposite lateral branches, which are correspondingly parallel to the two other spines ; the 

 proximal branches twice as long as the distal branches. 



Bimensixms. — Length of each spine 0"2, of the basal branches 0"07. 



Habitat. — Central Pacific, Station 271, depth 2425 fathoms. 



2. Triplagia triradialis, n. sp. 



Spines straight, of equal size and similar form, equidistant, three-sided prismatic, regularly pin- 

 nate, with six pairs of opposite pinnulce, tapering gradually towards the distal ends; the basal 

 pinnulge are again branched, with straight ramules. 



Dimensions. — Length of each spine 0"27, of the basal branches 0'08. 



Habitat. — Xorth Pacific, Station 256, surface. 



3. Tripilagia horizontalis, n. sp. 



Spines curved, cylindrical, irregularly branched, with three primary and nine to twelve 

 secondary branches, which are also slightly curved. The angles between the bases of the three 

 spines are equal, but the size and form of the branches different. 



Dimensions. — Length of the three spines 015 to 0'25, of the basal branches 0'05 to 0'08. 



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



Genus 385. Plagiacantha} Claparede, 1856, Monatsber. d. k. preuss. 

 Akad. d. Wiss. Berlin, November 13. 



Definition. — P 1 a g o u i d a with three radial spines, arising from one common 

 central point and corresponding to the edges of a three-sided pyramid. 



The genus Plagiacantha agrees with the preceding Triplagia in the simple 

 structure of the triradial skeleton, composed of three diverging radial spines, which are 

 united in a common centre at the oral pole of the central capsule. But whilst the 

 three radial rods of Triplagia lie in one horizontal plane, here they lie in different 

 planes and correspond to the tliree edges of a flat pyramid. Plagiacantha 

 arachnoides, described in 1856 by Claparede, was the earliest known form of aU 

 Plectoidea. 



' PlagiacantJia ^Heiving spines on the sides ; wTiay/of, SicauOa- 



