1240 THE VOYAGE OF H.M.S. CHALLENGER. 



3. Sethochytris pyramis, n. sp. 



Shell smooth, with slight collar stricture. Length of the two joints = 1:8, breadth = 1:5. 

 Cephalis ovate, with a conical horn of half the length. Thorax pyramidal, with three sharp edges ; 

 its base prolonged into three pyramidal, divergent, hollow, fenestrated feet, nearly as long as the 

 thorax. Pores regular, circular, doable-contoured. 



Dimensions. Cephalis - 04 diameter ; thorax 0'2 diameter, length of the feet 015. 



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



4. Sethochytris triangula, Haeckel. 



Lithochytris triangula, Bury, 1862, Polycystins of Barbados, pi. xix. fig. 7. 



Shell rough, with obliterated collar stricture (but distinct internal collar septum). Length of 

 the two joints = 1 : 6, breadth = 1:3. Cephalis subspherical, with a stout conical horn of the same 

 length. Thorax pear-shaped, inflated ; its base prolonged into three divergent, hollow, fenestrated 

 cones, about as long as the thorax. Pores regular, circular. 



Dimensions. Cephalis 0'03 diameter; thorax 0'09 diameter, length of the feet 01. 



Habitat. Fossil in Barbados. 



Genus 557. Clathrolychnus, 1 Haeckel, 1881, Prodromus, p. 431. 



Definition. S ethoperida (vel Dicyrtida triradiata clausa), with three vertical, 

 lateral latticed wings stretched between the apical horn and the three terminal feet. 

 The external lattice-work connecting the wings and closing the mouth forms an arachnoidal 

 mantle around the shell. 



The genus Clathrolychnus may be. derived directly from Clathrocorys, by develop- 

 ment of an external arachnoidal mantle connecting the three wings and the three feet, 

 and enveloping the whole shell, closing at the same time the basal mouth of the thorax 

 by a fenestrated plate. 



1. Clathrolychnus araneosus, n. sp. (PL 64, fig. 5). 



Cephalis subspherical, with irregular, polygonal pores and a large pyramidal horn of twice the 

 length. Length of the two joints = 4 : 9, breadth ='5 : 12. Thorax with three large triangular 

 holes (twice as broad as the cephalis) between the three pyramidal, divergent feet, which at the 

 distal end are connected by a narrow band of network, composed of two or three rows of polygonal 

 pores. The entire pyramidal shell is enveloped by a very delicate web of irregular, polygonal 



1 Clathrolychnus = Fenestrated lantern ; 



