EEPORT ON THE RADIOLARIA. 1203 



Thorax with three stout, curved, widely divergent ribs, prolonged into three cylindro-conical, curved 

 feet of twice the length, which are convex in the proximal half, concave in the distal half. Between 

 every two ribs, beyond the collar stricture, two large ovate meshes, and beyond this two rows of 

 smaller irregular meshes. 



Dimensions. Cephalis OD4 long, OD7 broad ; thorax 0'05 long, Oil broad. 



Habitat. Central Pacific, Station 268, depth 2900 fathoms. 



3. Sethopilium macropus, n. sp. (PI. 97, fig. 9). 



Shell smooth, with slight collar stricture. Eelative length of the two joints = 4:7, breadth = 6:13. 

 Cephalis hemispherical, with irregular double-contoured pores, about as broad as the bars. Thorax 

 with three very stout, curved, widely divergent ribs, prolonged into three curved, cylindrical, very 

 long feet, which are three to four tunes as long as the shell, and convex on the outside. Between 

 every two ribs, beyond the collar stricture, two large broad meshes, and beyond this two or three 

 rows of smaller meshes. 



Dimensions. Cephalis 0'04 long, 0'06 broad ; thorax 0'07 long, 013 broad. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



Genus 537. Lithomelissa, 1 Ehrenberg, 1847, Monatsber. d. k. preuss. 

 Akad. d. Wiss. Berlin, p. 54. 



Definition. S ethopilida (vel Dicyrtida triradiata aperta) with three free 

 lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. 

 Cephalis with one or more horns. 



The genus Lithomelissa, containing numerous and widely distributed forms, may like 

 Dictyophimus be regarded as one of the most primitive and ancient forms of Dicyrtida. 

 It differs from the latter by the lateral (not terminal) position of the three thoracic feet, 

 and may be derived either from Dictyophimus (by secondary development of intrapedal 

 network towards the mouth, on the inside of the three feet) or directly from Tripo- 

 spyris by similar formation of thoracic network beyond the collar stricture, outside the 

 base of the three divergent feet and pierced by the latter. As the species of this genus 

 are numerous, it may perhaps be better to divide it into two or three genera : Acromelissa, 

 with a single horn, Micromelissa, with two horns, and Sethomehssa, with three or more 

 horns. 



Subgenus 1. Acromelissa, Haeckel, 1881, Prodromus, p. 431. 

 Definition. Cephalis with a single occipital horn. 



1 Lithomelissa = Stone bee ; X/do?, ft&iavu. 



