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



Subgenus 2. Zygostephaniscus, Haeckel, 1881, Prodromus, p. 446. 



Definition. The two vertical rings of different heights; the frontal ring higher 

 than the sagittal ring, therefore with a sagittal constriction in the median plane. 



5. Zygostephanus reniformis, n. sp. 



Frontal ring kidney-shaped, in the upper half convex, in the lower half concave, in the latter 

 with a deep sagittal constriction, armed with numerous irregular short spines. Sagittal ring 

 thicker and lower, only two-thirds as high, with four pairs of short divergent spines (two ventral 

 and two dorsal pairs). 



Dimensions. Height of the frontal ring 013, hreadth 0'2. 



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



6. Zygostephanus violina, n. sp. 



Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal 

 constriction, armed with numerous irregular spines, which are partly simple, partly branched. 

 Sagittal ring thicker and lower, only half as high, with a few short conical spines at the apical and 

 hasal poles. 



Dimensions. Height of the frontal ring 012, breadth 018. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



7. Zygostephanus bicornis, n. sp. (PI. 93, fig. 2). 



Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal con- 

 striction ; its two halves pentagonal. Between numerous smaller spines there arise from the frontal 

 ring six groups of larger branched spines, two odd in the corners of the highest points (curved like 

 two horns), two branched pairs on the prominent lateral corners (at right and left), and two pairs in 

 the corners of the lowest points (like four branched basal feet). Sagittal ring only two-thirds as 

 high, with four pairs of irregular spines. 



Dimensions. Height of the frontal ring Oil, breadth 016. 



Habitat. South Pacific, Station 300, depth 1375 fathoms. 



Genus 415. Zygostephanium, 1 Haeckel, 1881, Prodromus, p. 446. 



Definition. C o r o n i d a with four large, partly latticed, lateral gates, without 

 basal gate. Skeleton composed of two meridional rings perpendicular to each other. 



The genus Zygostephanium differs from the preceding ancestral genus Zygostephanus 

 in the development of lattice-work along the two crossed rings, produced by their anasto- 

 mosing branches. Therefore the four large lateral gates between them, which are quite 

 simple, in the preceding genus here become more or less fenestrated. 



1 Zygostephanium = Small yoked ring ; vyoi>, 



