7t)8 THE VOYAGE OF H.M.S. CHALLENGER. 



to four pairs of strong conical teeth ; from the edges of the two smaller (sagittal) wings arise also 

 three to four pairs of teeth, but very short and broad, triangular ; each of these teeth bears on both 

 its (lateral) sides two opposite slender conical teeth, which are parallel to the large conical teeth 

 of the lateral wings. Therefore all teeth (eighteen to twenty-four) are placed opposite in pairs in 

 three parallel planes. Base of the spines pyramidal, with a small leaf-cross. The central capsule 

 of this large and very remarkable species commonly entirely includes the apophyses of the spines, 

 and is opaque, whitish. 



Dimensions. Length of the spines 0'2 to 0'3, breadth of the distal half O002 to 0'004, of the 

 proximal half O'Ol to 0'02. 



Habitat. Cosmopolitan ; Mediterranean, Atlantic, Pacific, surface. 



Subfamily 3. STAURACANTHIDA, Haeckel. 



Definition. Astrolouchida with a cross of four free apophyses (or four 

 crossed longitudinal rows of apophyses) on each radial spine. 



Genus 330. Xiphacantha, 1 Haeckel, 1862, Monogr. d. Eadiol., p. 384. 



Definition. A strolonchida with four simple apophyses on each radial spine, 

 opposite in pairs in the form of a cross. 



The genus Xiphacantha was founded by me iu 1862 for all those Acanthometrida 

 which bear simple or branched apophyses on their twenty equal spines. I restrict here 

 the genus to those Astrolonchida which bear on each spine a cross of four simple, not 

 branched, apophyses. These are either conical teeth or broad wings, sometimes extremely 

 thin leaves. Xiphacantha may be regarded as the ancestral form not only of the sub- 

 family Stauracanthida, but also of the Tessaraspida, derived from the latter. 



Subgenus 1. Xiphacanthonia, Haeckel. 



Definition. Apophyses of the radial spines small, formed like a tooth or a hook, 

 not wing-shaped. Edges of the spines commonly narrow, little prominent. 



1. Xiphacantha quadridentata, Haeckel. 



Xiphacantha quadridentata, Hacckol, 1862, Monogr. d. Radio!., p. 387, Taf. xviii. figs. I5a, 15I>. 

 Acanthomrtra quadridentata, J. Miiller, 1858, Abhancll. d. k. Akail. d. Wiss. Berlin, p. 48, 

 Taf. x. fig. 3. 



Spines slender, four-sided prismatic, gradually thinner towards the simple pyramidal apex. 

 I >ase with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, 

 smooth, about as long as the basal breadth of the spine. Central capsule opaque, reddish-brown. 



1 Xiphacantha = Sword spine ; Ji'fof, Ax,>i. 



