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



2. Icosaspis elegans, u. sp. (PI. 136, fig. 4 ; PI. 134, fig. 9). 

 Tessaraspis elegans, Haeckel, 1882, Manuscript et Atlas. 



Parmal meshes of very differeut size aud form ; iu the centre of each plate a cross of four 

 primary, pear-shaped " aspinal pores " (the largest of all) ; between them four secondary, little 

 smaller, crossed, egg-shaped " angular pores " ; around tliis rosette of eight larger meshes an inner 

 complete circle of sixteen to twenty polygonal coronal pores, and an outer incomplete circle of 

 thirty to forty very small marginal pores. The latter are smaller than the irregular sutural 

 meshes, which are constricted in the middle, about forty to sixty around each plate. Eadial spines 

 thin, cylindrical, or a little compressed ; their outer part longer than the inner. In this elegant 

 and very common species the condyles usually remain separated by sutures ; but sometimes the 

 latter become obliterated, and the whole shell then forms a single piece, Icosaspidium elegans. 



Dimensions. — Diameter of the shell 0-2 to 0-3, commonly 0-25 ; larger parmal pores 002, 

 smaller 0-01 to O'OOS ; sutural pores 0-005 to 0-015 ; bars 0-003. 



Habitat. — Tropical and Subtropical Atlantic, Canary Islands to Ascension Island, Stations 340 

 to 354, surface. 



3. Icosaspis cruciata, n. sp. (PI. 134, fig. 10). 



Parmal meshes very different ; iu the centre of each plate a cross of four primary, nearly 

 oblong, rectangular " aspinal pores " ; between these four secondary, triangular, egg-shaped " angular 

 pores " (the largest of aU), and around this rosette a single circle of twelve to twenty-four small 

 " coronal pores." The latter are of about the same size as the irregular sutural meshes, of which 

 there are twenty to thirty around each plate. Piadial spiines thin, cylindrical, or a little compressed ; 

 their outer part longer than the inner. 



Dimensions. — Diameter of the shell 0-2 to 0-3, connnonly 025 ; larger parmal pores 0025, 

 smaller 0-005 to O'Ol ; bars 0-005. 



Hahitat. — Tropical and Subtropical Pacific, Sandwich to Marquesas Islands, Stations 256 

 to 274, surface. 



4. Icosaspis ornata, n. sp. 



Parmal meshes very different ; in the centre of each plate a cross of four primary octagonal 

 aspinal pores (the largest of all) ; between them four secondary, rhombic angular pores, 

 aud around this rosette a circle of twelve to sixteen smaller, polyhedral coronal pores, which 

 are however larger than the irregular sutural pores (surrounding each plate to the number of twenty 

 to thirty). Radial spines thin, quadrangular, prismatic ; the outer part longer than the inner. 



Dimensions. — Diameter of the shell 025 ; larger parmal pores 003, smaller 001 ; sutural 

 pores 0-004 to 0-008 ; bars 0-006. 



Habitat. — South Pacific, Station 295, depth 1500 fathoms. 



