REPORT ON THE RADIOLARIA. 



921 



I. Subfamily 



Triplectida. 

 Three radial spines. 



II. Subfamily 



Tetraplectida. 

 Four radial spines. 



III. Subfamily 



Hexaplectida. 

 Six radial spines. 



IV. Subfamily 



Polyplectida. 

 Numerous radial spines. 



Synopsis of the Genera of Plectanida. 

 Three spines lying in one horizontal plane, . 

 Three spines corresponding to the edges of a flat pyramid, 



{All four spines equal, 

 One apical spine opposed to 

 three basal spines, 



Four spines arising in two pairs from the poles of a common 

 central rod; one apical spine different from three basal 

 spines, ....... 



Six spines arising from one common central point, . 



Six spines arising in two opposite groups from the poles of 

 a common central rod, ..... 



Numerous (seven to nine or more) radial spines arising from 

 a common centre (either a central point or a branched 

 rod), ....... 



393. Triplecta. 



394. Plectophora. 



395. Tetraplecta. 



396. Plectaniscus. 



397. Periplecta. 



398. Hexaplecta. 



399. Pledanium. 



400. Polyplecta. 



Subfamily 1. TKIPLECTIDA, Haeckel, 1881, Prodromus, p. 424. 

 Definition. P lectanida with three radial spines. 



Genus 393. Triplecta, 1 Haeckel, 1881, Prodromus, p. 424. 



Definition. P lectanida with three radial spines, arising from one common 

 central point and lying in one horizontal plane. 



The genus Triplecta is the simplest and most primitive of the Plectanida, and 

 may therefore be regarded as the prototype of this family. The skeleton represents 

 a triangular lattice-plate with three radial beams. On the central union of the latter 

 rests the oral pole of the central capsule. Since the axis of the latter is vertical, 

 the lattice-plate must be horizontal, serving for the expansion of the pseudopodia. 

 Triplecta has arisen from Triplagia by union of the branches of its three radial 

 spines. In the simplest case only three large meshes are formed, corresponding prob- 

 ably to the three cortinar meshes in the collar septum of many Cyrtellaria. 



1. Triplecta triangulum, n. sp. 



Spines straight, equal, smooth, cylindrical, each in the basal half with one pair of divergent 

 straight lateral branches. The opposed branches of every two neighbouring spines are united by a 



1 Triplecta = Hunting net with three beams ; TJ/J, TXSXTIJ. 



(ZQOL. CHALL. EXP. PABT XL. 1886.) Rr 116 



