1044 THE VOYAGE OF H.M.S. CHALLENGER. 



ancestral genera Cortina and Tripospyris, whilst the fourth is an odd anterior or sternal 

 foot, produced by anterior prolongation of the basilar segment of the sagittal ring. Here, 

 therefore, two opposed feet lie in the sagittal plane (a caudal and a sternal foot), whilst 

 the two others are the paired lateral or pectoral feet, as also in Stephanium and 

 Stephaniscus, p. 965. The Tetraspyrida ought not to be confounded with the 

 Therospyrida (sixth subfamily), in which the four feet have another signification. 



Subgenus 1. Tetrarrhabda, Haeckel, 1881, p. 429. 

 Definition. Feet simple, not branched nor forked. 



1. Tetraspyris stephanium, n. sp. (PI. 95, fig. 6). 



Shell nut-shaped, tuberculate, with deep sagittal stricture and small roundish pores ; three 

 pairs of larger pores on each side of the ring. Basal plate with four large collar pores. Apical 

 horn stout conical, half as long as the shell. Two pectoral feet somewhat longer than the two 

 sagittal feet, .one and a half times as long as the shell. All four feet straight, three-sided 

 prismatic, strongly divergent. 



Dimensions. Shell 008 long, 012 broad ; horn 0'04 long, feet 0'08 to 012 long. 



Habitat. Central Pacific, Station 272, depth 2600 fathoms. 



2. Tetraspyris cubica, n. sp. 



Shell nearly cubical, smooth, with slight sagittal stricture and small polygonal pores ; some 

 larger pores on both sides of the ring. Basal plate with four large collar pores. Apical horn 

 and the four feet of equal size and form, about as long as the shell, cylindrical in the basal, 

 spindle shaped in the distal half. 



Dimensions. Shell 0'09 diameter ; horn and feet 01 long. 



Habitat. Central Pacific, Station 265, depth 2900 fathoms ; also fossil in Barbados. 



Subgenus 2. Tetracorethra, Haeckel, 1881, Prodromus, p. 429. 

 Definition. Feet branched or forked. 



3. Tetraspyris tetracorethra, n. sp. (PI. 53, figs. 19, 20). 



Tetracorethra miraUlis, Haeokel, 1881, Prodromus, p. 429, and Atlas, loc. cit. 



Shell campanulate, tuberculate, with deep sagittal stricture and irregular polygonal pores ; two 

 pairs of larger pores at the flattened occipital face (fig. 20). Basal plate with four large collar 

 pores. Apical horn very long, thirty to forty times as long as the shell, slender three-sided 

 prismatic, straight, at the distal end irregularly branched, besom-shaped. Four basal feet half as 



