1510 THE VOYAGE OF H.M.S. CHALLENGER. 



9 



first and second joints together are conical, and about as long as each of the following joints. Cephalis 

 small, hemispherical, with a thick pyramidal horn of the same length. The fifth joint is the 

 broadest, the truncate mouth is slightly constricted (in the specimen figured it is broken off). 

 Pores regular, circular, quincunciaL 



Dimensions. Length of the shell (with eight joints) 0'2, breadth O'l ; length of each joint, 

 about 0'03. 



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



4. Spirocyrtis hemispira, n. sp. 



Shell slender, nearly spindle-shaped, three times as long as broad, without external strictures, 

 but with ten to eleven internal septa. The five or six upper of these are perfectly separate, com- 

 plete parallel rings ; the five or six lower are spirally connected. The eleven or twelve joints 

 gradually taper in length and breadth, from the broadest middle towards the two constricted ends 

 of the shelL The middle (fifth or sixth) joint is the broadest, and is three to four times as 

 broad as the constricted mouth. Cephalis small, hemispherical, with a conical horn of the same 

 length. Pores regular, circular, hexagonally framed. 



Dimensions. Length of the shell (with twelve joints) 0'25, breadth 0'09 ; length of the middle 

 joint 0-03. 



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



5. Spirocyrtis merospira, n. sp. (PI. 76, fig. 15). 



Shell ovate, with six to eight slight strictures, twice as long as broad. The three or four upper 

 joints are perfectly separated by annular septa, the three or four lower joints connected by an 

 internal spiral septum. The spiral line is often more or less irregular or interrupted (as is also the 

 case in the specimen figured). Mouth rather wide. Pores small, subregular, circular. A rather 

 variable species. 



Dimensions. Length of the shell (with eight joints) 0'2, breadth O'l. 



Habitat. Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms. 



6. Spirocyrtis diplospira, n. sp. (PL 76, fig. 17). 



Shell slender, ovate, with seven to eight slight strictures. All eight or nine joints are con- 

 nected by an internal double spiral septum, the first spiral beginning from the ventral side, the 

 second from the dorsal side of the collar stricture. Length and breadth of the single joints 

 rather variable and irregular ; the broadest joint is commonly the fifth. Mouth more or less con- 

 stricted. Pores subregular, circular. This remarkable species differs from all other Cyrtoidea 

 by the double spiral septum of the joints. 



Dimensions. Length of the shell (with eight joints) 0'2, breadth O'l. 



Habitat. Central Pacific, Station 274, depth 2750 fathoms. 



