1320 THE VOYAGE OF H.M.S. CHALLENGER. 



13. Pterocorys pi^ietta, n. sp. 



Shell thin-waUed, smooth, with two slight strictures. Length of the three joints= 1 : 6 : 3, 

 breadth = 1 : .3 : 1. Cephalis ovate, with a conical horn of twice the length. Thorax ovate, in the 

 middle zone with three conical wings of the same length, curved slightly downwards (Hke those of 

 Pterocorys colmnha, PI. 71, fig. 2). Abdomen constricted into a cylindiical tube half as long as the 

 thorax, with narrow mouth. Pores subregular, circular. 



Dimcnsimis. — Length of the three joints, a 0"02, h 0'12, c 0'06 ; breadth, a 0'02, l 0-06, c 0'02. 



Halitat. — Tropical Atlantic, Station 347, depth 2250 fathoms. 



Subgenus 3. Pterocorythium, Haeckel. 



Definition. — Horn of the cephalis double or multiple. Abdomen not prolonged into 

 a narrow^ tube. 



14. Pterocorys rhinoceros, n. sp. (PI. 71, fig. 1). 



Shell very delicate and thin-waUed, with two sharp strictures. Length of the three joints = 

 2 : 10 : 3, breadth, 3:11:9. Cephalis obtuse, conical, with two divergent, conical horns of equal 

 length. Thorax triangular, pyramidal ; from its three edges there arise on the middle joint three 

 conical descending wings (little larger than the horns), and from the base of each wing descend two 

 divergent crests, forming at the sides of the pyramid three rounded lobes. Abdomen short, 

 cylindrical, with wide, truncate mouth. Network of the whole shell very delicate, with very small 

 and numerous, regular, circular, hexagonally-framed pores. 



Dimension. — Length of the three joints, a 0-02, I 01, c 0-03 ; breadth, a 0-03, 6 Oil, c O'OO. 



Habitat. — Central Pacific, Stations 270 to 274, surface, and in various depths. 



15. Pterocorys prismatica, n. sp. 



Shell very delicate and thin-waUed throughout, with fine fenestration similar to that of the 

 preceding species, but difi'ering from it in the form of the abdomen, which is much larger, three- 

 sided and prismatic ; three edges of the prism decurrent from the bases of the three short wings. 

 Length of the three joints =:1 : 4 : 5, breadth = 2 : 6 : 6. No lobes at the thorax. Mouth wide 

 open, truncate, triangular. 



Dimensions. — Length of the three joints, a 0-02, b O'OS, c 01 ; breadth, a 0-04, b 012, c 012. 



Habitat. — South Pacific, Station 288, surface. 



16. Pterocorys tricornis, n. sp. 



Shell spiny, with two deep strictures. Length of the three joints = 1:5:3, breadth = 1:7:5. 

 Cephalis subspherical, with three stout, pyramidal, divergent horns, which are three times as long. 



