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



Dimensions, Eadius of each arm 012, basal breadth O'OIS, distal breadth 0'04. 

 Habitat. Fossil in the rocks of Barbados ; and living in the depth of the Central Pacific, 

 Station 268, depth 2900 fathoms. 



6. Histiastrum boseanum, n. sp. (PI. 46, fig. 1). 



Arms linear, twelve times as long as broad at their base (at their distal end twice as broad as 

 at their base), with rectilinear, parallel edges. The club-shaped end thickened, dentate, with two 

 lateral rows of strong teeth in the equatorial plane, and with one very stout, angular, terminal 

 spine. Central disk with two to three rings, broader than the arms. Patagium incomplete, with 

 four to five concave chamber-rows, enveloping only the basal half of the arms. I call this splendid 

 species in honour of Dr. Graf Bose, the great friend of nature and patron of the University of Jena. 



Dimensions. Eadius of each arm 0'25, basal breadth 0'02, distal breadth 0'05. 



Habitat. Indian Ocean, Madagascar, Eabbe. 



7. Histiastrum coronatum, n. sp. 



Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pi. iv. fig. 1. 



Arms linear, eight tunes as long as broad, with rectilinear parallel edges ; the thickened, nearly 

 spherical, distal end three times as broad, with five strong conical spines, one middle (perradial) 

 larger and two smaller on each side of it. Central disk with two to three rings, of the same 

 breadth as the' terminal knot of the arms. Patagium incomplete, square, enveloping the arms, with 

 the exception of the knot. 



Dimensions. Eadius of each arm 016, basal breadth 0'02, terminal breadth 0'06. 



Habitat Fossil in the rocks of Barbados. 



8. Histiastrum circulare, n. sp. 



Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pi. xxiii. fig. 1. 



Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with 

 ten to twelve strong terminal spines, the middle (perradial) larger, in all three tunes as long as 

 broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly 

 complete, circular, enveloping the whole arms, with exception of the outermost end. 



Dimensions. Eadius of each arm 0'22, basal breadth 0'02, terminal breadth 0'06. 



Habitat. Fossil in the rocks of Barbados ; and living in the depths of the Central Pacific, 

 Station 268, depth 2900 fathoms. 



9. Histiaslrum pentadiscus, n. sp. (PI. 46, fig. 2). 



Arms in their inner half linear, twice as long as broad, in their outer half circular, three times 

 as broad, with the same structure as the central disk, exhibiting three concentric rings around one 



