REPORT ON THE RADIOLARIA. 923 



3. Plectophora novena, n. sp. 



Spines slightly curved, three-sided prismatic, thorny, with two pairs of lateral branches. The 

 six smaller distal branches end freely, whilst the six larger basal branches are connected by slender 

 convex bows. There are therefore nine wide meshes, as in the preceding closely allied species. 



Dimensions. Length of the spines 0'18, of the basal branches 0'08. 



Habitat. North Atlantic, Fserb'e Channel (Gulf Stream) (John Murray), surface. 



4. Plectophora pyramidalis, n. sp. 



Spines straight, three-sided prismatic, with three to four verticils of short lateral branches. 

 The branches of the basal verticils are again ramified, and form by connecting bows a delicate loose 

 framework, covering the three sides of a flat^ pyramid, the three edges of which are the three radial 

 spines. 



Dimensions. Length of the spines 0'2, base of the pyramid 016. 



Habitat. Central Pacific, Station 267, surface. 



Subfamily 2. TETRAPLECTIDA, Haeckel, 1881, Prodromus, p. 424. 

 Definition. P leetanida with four radial spines. 



Genus 395. Tetraplecta, 1 Haeckel, 1881, Prodromus, p. 424. 



Definition. P leetanida with four equal radial spines, arising from one common 

 central point and corresponding to the four axes of a tetrahedron. 



The genus Tetraplecta has been derived from Tetraplagia by union of the neighbour- 

 ing branches of the four radial spines, diverging from a common point in different 

 directions. In some forms of this genus the four rods seem to correspond exactly to 

 the four axes, which are directed from the centre of a tetrahedron towards its four 

 corners ; whilst in other forms the four rods and the angles between them are perhaps 

 not perfectly equal. 



1. Tetraplecta tetrahedra, n. sp. 



Spines straight, equal, three-sided prismatic, pinnate, each with three or four pairs of opposite 



straight slender pinnulae or lateral branches ; the pinnulae of each side are correspondingly parallel. 



1 Tetraplecta = Hunting net with four beams ; 



