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



vertical feet, but also upwards into two curved bows, which are united in a vertical ascending 

 horn, arising from the apical pole of the sagittal ring. 



Dimensions. — Diameter of the culje 014 ; total height 0-21. 



Hcibitat. — Central Pacific, Station 265, depth 2900 fathoms. 



Subgenus 3. Tnj^ocuhus, HaeckeL 



Definition. — Basal ring with three descending feet (one odd caudal and tvi^o 

 paired lateral). 



6. Acrocuhiis lasanum, n. sj). 



Mitral ring smaller than the liasal, both rings square, with curved rods. Sagittal ring ovate, 

 prolonged upwards into an occipital simple horn, downwards into a caudal foot. Two lateral 

 columella? prolonged downwards into two pectoral feet. All three feet conical, about as long as 

 the height of the cube. 



Dimensions. — Diameter of the cube 0"08 ; length of the feet 0"07. 



Hahitat. — North Pacific, Station 241, depth 2300 fathoms. 



7. Acrocuhus corlina, n. sp. (PL 93, fig. 16), 



Mitral ring smaller than the basal, both rings elliptical, with curved rods. Sagittal ring 

 ovate, prolonged upwards into an occipital horn, downwards into a caudal foot, as in the preceding 

 species. As in the latter, also, the two lateral columella? are prolonged downwards into two 

 pectoral feet, but also upwards into two convergent horns, which are united with the occipital 

 horn (commencing the formation of a galea). Eings and feet somewhat thorny. 



Dimensions. — Diameter of the cube 016 ; total height 0'2. 



Habitat. — Central Pacific, Station 266, depth 2750 fathoms. 



Subgenus 4. Tetracuhus, HaeckeL 

 Definition. — ^Basal ring with four descending feet (two sagittal and two lateral). 



8. Acrocuhus tetrapodius, n. sp. ' 



Mitral and basal rings of the same size, square, with straight rods, sagittal ring also square. 

 The four vertical columellce are nearly parallel and straight, prolonged upwards into four short 

 conical horns, downwards into four longer conical feet. (The shell has nearly the form of a 

 geometrical cube, the eight corners of which are prolonged into eight vertical conical spines, 

 four smaller ascending and four larger descending.) 



Dimensions. — Diameter of the cube 0"09 ; length of the feet 0'06. 



Hahitat. — South Atlantic, Station 332, depth 2200 fathoms. 



