REPORT ON THE RADIOLARIA. 887 



denticulate incisions. Diameter of its mouth one-third as long as the whole shell and somewhat 

 smaller than the equatorial diameter. Hydrotomical spines about twice as long as their sheath, 

 pyramidal, with emarginate point and six wings. Geotomical spines short and strong, pyramidal. 

 Sixteen other spines thin, straight, conical. 



Dimensions. Length of the shell 0'3 ; equatorial breadth Oil, polar breadth 01. 



Habitat. Central Pacific, Station 266, surface. 



Genus 381. Diplocolpus? n. gen. 



Definition. Diploconida with only two developed, very large spines 

 (opposite in the hydrotomical axis); all the other eighteen spines quite rudimentary 

 or externally atrophied. 



The genus Diplocolpus is the last and the most modified genus among the 

 ACANTHARIA. The eighteen smaller spines of Diploconus are here quite rudimentary or 

 have even perfectly disappeared by atrophy, so that the shell seems to consist only of 

 the large hydrotomical spines and their enveloping sheaths. 



Subgenus 1. Diplocolpulus, Haeckel. 



Definition. Mantle of the double cone not compressed ; its transverse section 

 therefore circular. 



1 



. Diplocolpus costatus, n. sp. (PL 140, fig. 7). 



Mantle of the double cone thin walled, not compressed ; its transverse section circular or nearly 

 hexagonal ; its contour little convex ; surface with six thick longitudinal equidistant ribs and 

 many thinner ribs between them ; margin denticulate. Transverse diameter of the shell one- 

 third as long as the longitudinal. The two hydrotomical spines thick and short, little prominent 

 over the polar mouth. No rudiments of other spines visible externally. 



Dimensions. Length of the shell 015 ; equatorial and polar breadth 0'05. 



Habitat. Indian Ocean (Madagascar), Eabbe, surface. 



2. Diplocolpus cristatus, n. sp. (PL 140, fig. 6). 



Mantle of the double cone thick walled, not compressed ; its transverse section circular or 

 hexagonal ; its contour nearly straight ; surface with six thick prominent longitudinal equidistant ribs ; 

 margin irregularly dentated. Transverse diameter of the shell half as long as the longitudinal. 



1 Diplocolpus Double bosom; SCZ-AG'O?, xo'ATrof. 



