1152 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Pteroscenium differs from the preceding Archiscenium only in the 

 ramification of the internal columella, and therefore exhibits to it the same relation 

 that Cladoscenium bears to Euscenium. The branches of the columella form also here 

 verticils of ascending branches, three in each verticil, and their distal ends are inserted 

 on the inner surface of the lattice-shell. 



1. Pteroscenium arcuatum, n. sp. (PI. 98, fig. 4). 



Shell campanulate, smooth, nearly conical, somewhat broader than long, with irregular dense 

 network of small circular pores. Columella straight, with two or three triradiate verticils of 

 horizontal lateral branches, which are inserted in the shell-wall. Horn slender pyramidal, as long as 

 the shell. Three divergent feet twice as long as the horn, strongly curved, thorny, three-edged ; the 

 distance of their pointed ends twice as broad as the shell. From the outer edge of each foot arise 

 numerous ascending bristles, which are connected together and with similar lateral branches of the 

 horn by curved arches, forming three dehcate spiny vertical wings. 



Dimensions.- — Shell 0-06 long, 0"08 broad. 



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



2. Pteroscenium arcadophorum, n. sp. 



Shell campanulate, smooth, with irregular polygonal pores, very similar to the preceding species 

 but with much broader wings, forming several arcades with three to five rows of irregular meshes. 

 Columella with five or six triradiate verticils of lateral branches. Horn twice as long as the shell, 

 of the same length as the strongly curved spinulate feet. 



Dimensions. — Shell 0'09 long. Oil broad. 



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



3. PterosceniuTn pinnatum, n. sp. (PI. 53, figs. 14, 15, 16). 



Shell campanulate, smooth, somewhat longer than broad, with irregular dehcate network of 

 sniaU roundish pores. Columella straight, with numerous (eight to twelve) triradiate verticils of 

 ascending lateral branches, which are inserted in the shell-wall. The uppermost end of the 

 columella is a conical apical horn. The three divergent feet are smooth, slender, conical, sUghtly 

 curved, about as long as the shell, pinnate, with six to ten pairs of ascending lateral branches, 

 parallel to those of the columella and inserted on the three vaulted lateral wings. (Fig. 14 exhibits 

 the outside of the shell, fig. 15 the internal structure of the cortina, fig. 16 the basal view.) 



Dimensions. — Shell 01 long, 012 broad. 



Habitat— Central Pacific, Station 274, depth 2750 fathoms. 



4. Pteroscenium spinulosum, n. sp. 



Shell campanulate, spinulate, about as long as broad, with small and numerous irregular 

 polygonal pores, very similar to the preceding species, Ijut differing in the more slender form of 



