1360 THE VOYAGE OF H.M.S. CHALLENGER. 



three wings arise by a broad, triangular, striated base from the upper half of the abdomen, below 

 the lumbar stricture. The cephalic horn and the three divergent wings are shorter, and at the 

 distal end not so much thickened as in Theopera cortina. 



Dimensions. Length of the three joints, a 0'025, 1 0'045, c 012 ; breadth, a 0'03, b 0'07, c 008. 



Habitat. Tropical Atlantic, Station 347, depth 2250 fathoms. 



4. Rhopalocanium pythia, n. sp. 



Rhopalocanium ornaturn, Bury, 1862, Polycystins of Barbados, pi. vi. fig. 1. 



Shell nearly ovate, with two deep strictures. Length of the three joints = 1:4:8, breadth = 

 1:4:4. Cephalis subspherical, with a conical horn of three times the length. Thorax inflated, 

 abdomen inversely campanulate and prolonged into a short, conical, latticed tube. Pores sub- 

 regular, circular. Three wings slender, as long as the abdomen, arising by a broader base from the 

 uppermost part of the abdomen, their thickened end being curved inwards. 



Dimensions. Length of the three joints, a 0'02, b 0'07, c 015 ; breadth, a 0'03, b 0'08, c 0'07. 



Habitat. Fossil in Barbados. 



5. Rhopalocanium delphicum, n. sp. (PL 67, fig. 9). 



Shell nearly spindle-shaped, with two deep strictures. Length of the three joints = 1:2:4, 

 breadth =1:3:3. Cephalis hemispherical, with a slender, conical, curved horn, as long as the 

 hemispherical thorax. Abdomen inversely campanulate, prolonged into a short, conical, latticed tube. 

 Pores subregular, circular. Three wings arising by a narrow base from the uppermost part of the 

 abdomen, slender, cylindrical, S-shaped, curved, divergent, with a thick scaly appendix like a fir- 

 cone at the distal end. 



Dimensions. Length of the three joints, a 0'025, b 0'07, c 014 ; breadth, a 0'03, b 0"09, c O'OS. 



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



Genus 599. Rhopalatractus, 1 Haeckel, 1881, Prodromus, p. 437. 



Definition. T heoperida (vel Tricyrtida triradiata clausa) with three lateral 

 wings on the sides of the inversely conical abdomen, which bears a vertical terminal 

 horn on the basal apex. 



The genus Rhopalatractus, one of the most remarkable forms of Tricyrtida, differs 

 from the preceding Rhopalocanium, its ancestral form, in the production of a vertical, 

 basal horn, which descends from the basal apex of the inversely conical abdomen, and 

 is opposed to the upper apical horn of the cephalis. The shell becomes here, therefore, 

 exquisitely spindle-shaped. 



1 Rliopalatractut = Spindle with clubs ; 



