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



Subgenus 1. Astracturium, Haeckel. 

 Definition. Distal end of the arms blunt or truncated, without terminal spines. 



1. Astractura ordinata, n. sp. 



? Astromma sp., Bury, 1862, Polycystins of Barbados, pi. xiv. fig. 3. 



Phacoid shell three times as broad as the medullary shell, with six pores on its radius, without 

 a completely developed chambered ring. Arms trapezoidal, somewhat longer than the radius of the 

 disk, at the truncated distal end as broad as long, at the base one-third smaller. 



Dimensions. Diameter of the phacoid shell 0'08, of the medullary shell 0'03 ; length of the 

 arms 0'05, distal breadth 0'05, basal breadth 0'035. 



Habitat. Tropical Atlantic, Station 348, depth 2450 fathoms ; also fossil in Barbados. 



2. Astractura clavigera, n. sp. 



Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pi. iv. fig. 2. 



Phacoid shell twice as broad as the medullary shell, with ten pores on its radius, surrounded 

 by one perfect chambered ring. Arms club-shaped, about as long as the radius of the central 

 disk, at the rounded distal end two-thirds, at the base one-third as broad as long. 



Dimensions. Diameter of the phacoid shell 01, of the medullary shell 0'05 ; length of the 

 arms 0'06, basal breadth 0'02, distal breadth 0'04. 



Habitat. Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms ; fossil in 

 the rocks of Barbados. 



Subgenus 2. Astractinium, Haeckel. 

 Definition. Distal end of the arms furnished with a radial spine. 



3. Astractura aristotelis, Haeckel. 



Astromma aristotelis, Ehronberg, 1856, Microgeol., Taf. xxxvi. fig. 32; AbhanJl. d. k. Akad. 



d. "Wiss. Berlin, 1875, p. 66, Taf. xxx. fig. 4. 

 Astromma aristotelis, Haeckel, 1862, Monogr. d. Eadiol., p. 489. 

 1 Astromma aristotelis, Bury, 1862, Polycystins of Barbados, pi. xiv. fig. 4. 



Phacoid shell three times as. broad as the medullary shell, with six to eight pores on its radius, 

 surrounded by one perfect chambered ring. Arms nearly trapezoidal, about as long as the diameter 

 of the central disk, at the base half as broad, at the truncated distal end nearly as broad as long, 

 and armed with a large pyramidal terminal spine. Each arm with about eight transverse and 

 longitudinal rows of chambers. 



