REPOET ON THE RADIOLAEIA. 549 



The genus Stephanastrum, founded (1847) by Ehrenberg for the very peculiar 

 Stephanastrum rhomhus, diifers from the ];iearly allied foregoing genera in the 

 imperfect development of the peculiar jjatagium, connecting only the distal ends of the 

 four arms, while it is absent at their base. Two new species, different from 

 Stephanastrum rhomhus by the regular square form, were found in the Challenger 

 collection. 



Subgenus 1. Stephanastrella, Haeckel. 

 Definition. — All four arms of the cross have the same size. 



1. Stephanastrum quadratum, n. sp. (PI. 46, fig. 5). 



All four arms of the same size, six times as long as broad at their base, ending with a strong, 

 short, four-sided jiyramidal spine. In the outer half of each arm are two opposite lateral spongy 

 wings, which form an equilateral triangle, and from union of the bases of the four triangles arises the 

 peculiar patagium, which forms a square with four large interbrachial ojjenings. 



Dimensions. — Eadius of each arm 0'25, basal breadth 0-035 ; length of the sides of the square 

 patagium 0'3. 



Habitat. — Pacific, central area, Station 268, depth 2900 fathoms. 



2. Step)hanastrum capitatum, n. sp. (PI. 44, fig. 1). 



All four arms of the same size, five times as long as broad at their base, at their distal end with 

 a spongy, nearly spherical capitulum of twice their breadth, provided with a very strong, angular, 

 pyramidal, terminal spine (half as long as the arm). All four arms connected by a square 

 patagium, arising immediately below the cajjitula, and perforated by four large interbrachial 

 openings. 



Dimensions. — Eadius of each arm (without the terminal spine) 0'25, basal breadth 0"05 ; length 

 (jf the sides of the square patagium O'o. 



Habitat. — Pacific, central area, Station 265, depth 2900 fathoms. 



Subgenus 2. Stephanastromma, Haeckel. 

 Definition. — Two opposite arms of the cross larger than the two others. 



3. Step)hanastrum rhomhus, Ehrenberg. 



Stephanastrum rhomhus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 33; Abliandl. d. k. Akad. 

 d. Wiss. Berlin, 1875, Taf. xxv. fig. 1. 



Two arms of the longitudinal axis one and a third times as long as two arms of the transverse 

 axis. All four arms linear, about eight times as long as broad, at their distal end somewhat 



