REPORT ON THE RADIOLARIA. 909 



1. Triplagia primordialitt, n. sp. (PL 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. 



Dimensions. Length of each spine O2, 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 pinnulse, tapering gradually towards the distal ends ; the basal 

 pinnulse are again branched, with straight ramules. 



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



Habitat. North Pacific, Station 256, surface. 



3. Triplagia 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 0'15 to 0'25, of the basal branches 0'05 to 0'08. 



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



Genus 385. Plagiacantha, 1 Claparede, 1856, Monatsber. d. k. preuss. 

 Akad. d. Wiss. Berlin, November 13. 



Definition. Plagonida 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 three edges of a flat pyramid. Plagiacantha 

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

 Plectoidea. 



1 Plagiacantha = Having spines on the sides ; ***y/of, x9a- 



