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



prolongations of the four internal beams) alternating with four interradial spines arising from the 

 margin of the disk. 



Dimensions. Diameter of the disk (with five rings) 0'13; breadth of each ring O014; 

 pores 0-003. 



Habitat. Fossil in the rocks of Barbados. 



Genus 222. Stylochlamydium? Haeckel, 1881, Prodromus, p. 460. 



Definition. P orodiscida with numerous (five or more, commonly eight to 

 twelve) solid radial spines, regularly or irregularly disposed on the margin of the 

 circular or polygonal disk ; margin of the disk surrounded by a thin, porous (but not 

 chambered), equatorial girdle. 



The genus Stylochlamydium is intermediate between Perichlamydium (with which 

 it was formerly united) and Stylodictya. It deals with the former in the peculiar 

 equatorial girdle, with the latter in the radial spines of the disk margin, which pierce the 

 girdle. To both these genera it shows slow transitions, and can hardly be subjected to 

 a sharp definition. 



Subgenus 1. Stylochlamys, Haeckel. 

 Definition. All rings of the disk concentric, circular (or somewhat polygonal). 



1. Stylochlamydium asteriscus, n. sp. (PI. 41, fig. 10). 



Pemclilamydium asteriscus, Haeckel, 1879, MS. 



All rings of the disk concentric, circular, or polygonal, with increasing breadth from the centre ; 

 the fifth ring twice as broad as the second. Pores irregular, roundish, three to four on the breadth 

 of each ring ; in the rings two to six times as large as in the equatorial girdle, which is half as 

 broad or two-thirds as broad as the radius of the disk. Twelve bristle-shaped radial spines are 

 connected by the girdle near to the points; four crossed spines arising from the central chamber; 

 two others between these in each quadrant arising from the first ring. 



Dimensions. Diameter of the disk (with five rings) - 15, with the girdle 0'25 ; breadth of the 

 second ring O'Ol, of the fifth ring 0'02 ; pores O'OOl to 0'005. 



Habitat. Pacific, central area, Station 272, depth 2600 fathoms. 



2. Stylochlamydium limbatum, Haeckel. 



Peric/ihtmydium limbatum, Ehrenberg, 1847, MonatsLcr. d. k. preuss. Akad. d. Wiss. Berlin, 



p. 43; Mikrngeol., 1854, Taf. xxii. tig. 20. 

 Pericldaiiiydium limbatum, Haeckel, 1862, Monogr. d. EadioL, p. 494. 



All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two on the 



breadth of each ring; twice to three times as large as the fine pores of the equatorial girdle, which is 



1 Stylochlamydium = S\ie\l with styles and mantle ; ori/Xof, 



