REPORT ON THE RADIOLARIA. 755 



Genus 327. Phractacantha? Haeckel, 1881, Prodromus, p. 465. 



Definition. A strolonchida with two branched, but not latticed, opposite 

 upophyses on each radial spine. 



The genus Phractacantha differs from its ancestral form, the preceding Litho- 

 phyttiwm, by the ramification of the apophyses, which are either forked or bear 

 lateral branches. If the prolonged fork-branches of the neighbouring spines meet 

 and form a lattice -shell, this genus passes over into Phractaspis, the common ancestral 

 form of the Diporaspida. 



1. Phractacantha bifurca, n. sp. 



Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base 

 pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses ; 

 ends of the fork branches acute. 



Dimensions. Length of the spines O'l, breadth 0'006. 



Habitat. Central Pacific, Station 274, surface. 



2. Phractacantha bipennis, n. sp. 



Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex 

 simple. Base pyramidal, without leaf-cross. From the middle arise two opposite broad, forked 

 apophyses ; ends of the fork-branches broad and obtuse. 



Dimensions. Length of the spines 015, breadth in the middle 0'012. 



Habitat. Central Pacific, Station 266, surface. 



Genus 328. Doracantha? Haeckel, 1881, Prodromus, p. 465. 



Definition. A strolonchida with two latticed or fenestrated apophyses on 

 each radial spine. 



The genus Doracantha arises from the foregoing Phractacantha by union of 

 the fork -branches of the apophyses on each spine. By this concrescence is formed a 

 polygonal or roundish plate with two pores, pierced by the radial spine between them. 

 Doracantha may be regarded as a Dorataspis, in which the twenty small fenestrated 

 plates have not become united. 



1 f'hractacaiitha = Spines enclosed by aliedge; <Pc*ToV, xxaci/f. 



2 Doracantha = Spear-like spine; 8t-, cix.aia6a. 



