846 THE VOYAGE OF H.M.S. CHALLENGER. 



pores and an incomplete corona of thirty to forty very small marginal pores ; the latter are not to 

 be distinguished from the pores of the obliterated sutures. Eadial spines quadrangular, the outer 

 pyramidal part shorter than the inner prismatic part. Condyles grown together. As the plates are 

 quite even, the shell becomes icosahedral. 



Dimensions. Diameter of the shell 016, pores 0'002 to 0'02, bars 0'005. 



Habitat. North Pacific, Station 241, surface. 



9. Icosaspis icosastaura, n. sp. (PI. 136, fig. 3). 



Tessaraspis icosastaura, Haeckel, 1882, Manuscript et Atlas. 



Parmal plates of different size and form ; in the centre of each plate a cross of four larger 

 primary, pyriform aspinal pores ; between these four smaller roundish angular pores, and around 

 this rosette a circle of ten to twenty (commonly sixteen) coronal pores, little larger than the very 

 small sutural pores. Eadial spines very thin and long, cylindrical or bristle-shaped. Condyles 

 grown together ; no suture visible. 



Dimensions. Diameter of the shell 014 ; larger pores of the cross O'Ol, smaller pores (V002 to 

 0-008 ; bars 0'002 to 0'004. 



Habitat. Central Pacific, Station 268, surface. 



Genus 365. Hylaspis, 1 n. gen. 



Definition. Dorataspida with twenty plates, which are perforated by one 

 hundred and sixty to three hundred or more parmal pores (in each plate four crossed 

 aspinal pores, and around them four to twelve or more coronal pores). Surface covered 

 with numerous by-spines. 



The genus Hylaspis exhibits the same structure of the shell as the nearly allied 

 ancestral genus Icosaspis, and differs from it only in the development of by-spines. Some 

 species of these two genera exhibit the highest degree of complication in the structure 

 of the shell seen among the Dorataspida. 



1. Hylaspis serrulata, n. sp. (PL 135, fig. 1). 



Parmal meshes four hundred to five hundred ; in the centre of each plate a cross of four very 

 large pentagonal or roundish aspinal pores, and around this a circle of sixteen to twenty much 

 smaller irregular, polygonal, coronal pores ; the latter of about the same size as the sutural pores. 

 On each condyle one thin zigzag-shaped by-spine, nearly as long as the radius. Twenty radial 

 spines very long, quadrangular, prismatic ; on the inside thinner and smooth, on the outside 

 thickened, and armed with four rows of recurved teeth, serrated. 



Dimensions. Diameter of the shell 018, aspinal spines 0'02, other pores 0'002 to O'Ol, bars 

 0-003. 



Habitat. South Atlantic, Station 326, surface. 



shield ; i'Xu, doxi;. 



