1140 THE VOYAGE OF H.M.S. CHALLENGER. 



scattered, of very different sizes. Three lateral wings, stout, prismatic, about as long as the shell 

 widely divergent and S-shaped, curved. 



Dimensions. Shell O08 diameter, wings O'OS long. 



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



3. Archipilium cyrtopterum, n. sp. 



Shell ovate, rough, twice as broad as the constricted month. Pores small and numerous, 

 subregular, circular, smaller than the bars. Three lateral wings cylindrical, crescentic, in the upper 

 half divergent, in the lower convergent, one and one-half times as long as the shell. 



Dimensions. Shell 0'09 long, 0'07 broad ; wings 014 long. 



Habitat. Central Pacific, Station 265, depth 2900 fathoms. 



Genus 501. Tripilidium, 1 Haeckel, 1881, Prodromus, p. 428. 



Definition. A rchipilida (vel Monocyrtida triradiata aperta) without lateral 

 ribs, with three simple or branched terminal feet and an apical horn. 



The genus Tripilidium differs from Tripodonium in the absence of the three 

 lateral ribs, and may be derived either from this ancestral form, or directly from 

 Tripospyris (by loss of the sagittal ring and constriction); perhaps also from Lychno- 

 canium (by reduction of the cephalis). We distinguish as two subgenera Tristylocorijs 

 (with simple feet) and Tripodocorys (with branched feet). 



Subgenus 1. Tristylocorys, Haeckel. 

 Definition. Feet simple, not branched. 



1. Tripilidium cortina, n. sp. 



Shell campanulate, rough, about as long as broad. Pores subregular, circular, larger in the middle 

 zone, twice to three times as broad as the bars. Mouth constricted, half as broad as the shell. 

 Apical horn straight and stout, three-sided pyramidal, about as long as the shell. Three feet 

 divergent, slightly S-shaped, curved, somewhat longer than the shell. 



Dimensions. Shell 01 diameter, horn 0'09 long, feet 0'13 long. 



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



2. Tripilidium hemisphcericum, n. sp. 



Shell hemispherical; smooth, nearly twice as broad as long. Pores large, with thin bars, 

 irregular, roundish, of very different sizes. Mouth wide open. Apical horn conical, half as long as 



1 Tri'fiiliditcm = Small hat with three feet ; TJ<, xihtiiov. 



