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



10. Tessaraspis irregularis, n. sp. 



Parmal meshes irregular, roundish, of unequal size, three to six times as Ijroad as the Ijars, and 

 on an average larger than the irregular sutural meshes. Eadial spines cylindrical, the outer part 

 longer than the inner part. 



Dvmrnsions. — Diameter of the shell OlS, parmal pores 0'006 to 0'012, sutural pores 0'005 to 

 0-01 ; bars 0-002. 



Habitat. — Central Pacific, Station 270, surface. 



Subgenus 2. Tessaraspidium, Haeckel. 



Definition. — Condyles of the neighbouring plates grown together and sutures 

 obliterated ; therefore the whole shell forms a single piece of acanthin. 



11. Tessaraspis quadrata, n. sp. 



Tessaraspidium quadrat am, Haeokel, 1882, Manuscript. 



Parmal meshes square, four times as broad as the thin l:)ars, on an average of the same size as 

 the polygonal sutural meshes. Eadial spines stout, tetrapterous, prismatic, in the outer part longer 

 than in the inner. Sutures of the shell completely obliterated, therefore the whole shell forms one 

 piece. 



Dimensions. — Diameter of the shell 0'16, of the parmal pores 0'012, sutural pores O'Ol to 0'015. 



Habitat. — South Atlantic, Station 332, depth 2200 fathoms. 



12. Tessaraspis rotunda, n. sp. 



Parmal meshes circular, of equal size, twice as broad as the thick bars, on an average smaller 

 than the roundish sutural meshes. Eadial spines cylindrical in the inner part, which is somewhat 

 longer than the outer conical part. Sutures of the shell completely obliterated, therefore the 

 whole shell forms one piece. 



Dimensions. — Diameter of the shell 0'12, parmal pores 0"008, sutural pores 0'005 to 0'015. 



Habitat. — North Atlantic, Station 354, surface. 



13. Tessaraspis concreta, n. sp. (PI. 136, fig. 5). 



Parmal meshes irregular, polygonal or roundish, six to eight times as broad as the narrow and 

 high bars, much larger than the irregular sutural meshes. Eadial spines leaf-shaped, compressed, 

 two-edged, pointed at both ends ; inner and outer part nearly of equal size. Shell very thick 

 walled ; meshes therefore funnel-shaped ; sutures completely obliterated, therefore the whole shell 

 forms a single piece. 



Dimensions. — Diameter of the shell 0-09, parmal pores 0-02, sutural pores 0-01. 



Habitat. — Central Pacific, Station 274, depth 2750 fathoms. 



