REPOET ON THE RADIOLAEIA. 1153 



the horn and the feet, bearing more numerous lateral branches (twelve to sixteen pairs on each 

 foot). Columella with six to eight triradiate verticils. Horn about as long as the shell. 



Dimensions. — Shell 01 long, 01 broad. 



Hahitat. — Central Pacific, Station 268, depth 2900 fathoms. 



5. Pteroscenium macropodium, n. sp. 



Shell campanulate, spinulate, with irregular polygonal pores ; very similar to the two preceding 

 species, but differing in the size and shape of the three feet, which are for the most part solid, 

 triangular, nearly parallel, vertical, very slender, three times as long as the shell, latticed only at 

 the curved base, with few pairs of lateral branches. Columella with four to six triradiate verticils, 

 as long as the stout triangular pjTamidal horn. 



Dimensions. — Shell 01 long, O'OS broad. 



Habitat. — Central Pacific, Station 272, depth 2600 fathoms. 



6. Pteroscenium tripocolpum, n. sp. 



Shell campanulate, spinulate, similar to Emcenium tricolpiuvi (PL 53, fig. 12) with three vaulted 

 hemispherical bosoms between the three delicate arachnoidal vertical wings. Network loose, very 

 irregular, with polygonal meshes of very different sizes. Columella with three or four trii-adiate 

 verticils, as long as the slender pyramidal horn. Three feet twice as long, somewhat curved, widely 

 divergent, with three or four pairs of lateral branches. The three edges of the feet and of the horn 

 are elegantly denticulated. 



Dimensions. — Shell 0-06 long, 0-09 broad. 



Habitat. — Central Pacific, Station 266, depth 2750 fathoms. 



Genus 508. Peridium,^ Haeckel, 1881, p. 429. 



Definitioyi. — Ar ch ip er i da (vel Monocyrtida triradiata clausa) without internal 

 columella, with an apical horn. 



The genus Peridium (or Archiperidium, Prodromus, loc. cit.) and the two following 

 nearly allied genera form together the small group of Ai-chibursida, differing from the 

 four preceding genera (the Euscenida) in the absence of an internal free columella. 

 The three basal feet have therefore no direct connection with the apical horn. 

 Peridium, the ancestral form of the Archibursida, may have originated either from 

 Euscenium by reduction and loss of the columella, or directly from Tripospyris by loss 

 of the sagittal ring and the longitudinal constriction. 



Subgenus 1. Peridarium, Haeckel. 

 Definition. — Feet smooth, simple, neither spiny nor branched. 



1 Peridium = Small pouch ; itdj/B/oi/. 

 (ZOOL. CHALL. EXP. — PART XL. — 1886.) Rr 145 



