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



The genus Lithomespilus differs from the closely allied ElUiosoxvphus in the further 

 differentiation of both poles of the main axis. One ^jole exhibits only a single polar 

 spine, the other pole a group of several spines, peculiarly grouped together. It differs 

 from the similar Sphoeroviiespilus (PI. 14, figs. 12, 13) in the ellipsoidal form of the shell. 



1. Litliomespilus phloginus, n. sj). (PL 14, fig. 16). 



Proi^ortion of the major axis of the ellipsoid to the minor = 4:3. Shell thick walled, with 

 circular pores of different size, the breadth of which equals that of the bars ; twelve to fifteen pores 

 on the half equator. Surface smooth, with the exception of a circumpolar region covered with 

 numerous thick spines of unequal size, which surround the large single polar spine and are curved 

 like a bow against its axis. This larger polar spine is straight, and equals in length the major axis of 

 the shell. The other and opposite polar spine is scarcely one-fourth as long, perfectly simple, very 

 stout, and of a three-sided pyramidal shape. 



Biviensions. — Longer axis of the ellipsoidal shell 0'08, shorter axis 006 ; pores 0'002 to O'OOC, 

 bars 0-003 to O'OOo ; length of the polar spines — longer 0'08, shorter 0'02. 



Habitat. — Indian Ocean, near Madagascar, depth 1200 fathoms, Smith. 



2. Lithomespihis jMogoidea, u. sp. (PI. 14, fig. 17). 



Proportion of the major axis to the niinor = 5:4. Shell very thick walled, with roundish, 

 double-contoured pores of different size and form, twice to three times as broad as the bars ; sixteen 

 to eighteen pores on the half equator. Surface smooth, with the exception of a circumpolar region 

 covered with numerous thin sjjines of unequal size, which surround the large single polar spine and 

 are curved like a bow against its axis. This larger polar spine is straight, and equals half the size 

 of the major axis of the shell ; the other polar spine (sometimes double, as in the figured specimen) 

 is much shorter, being scarcely one-fourth as long. 



Dimensions. — Longer axis of the shell 0'08, shorter axis 0-065 ; pores O-QOS to 0-006, bars 0-002 

 to 0-004 ; length of the polar spines — longer 0-04, shorter 0-01. 



Habitat. — Central area of the Pacific, Stations 2*70 to 272, depth 2425 to 2925 fathoms. 



3. Lithomespilus Jlammeus, n. sp. 



Stylosplicera species, Bury, 1862, Polycystins of Barbados, pi. xi. tig. 3. 



Proportion of the major axis to the minor = 4:3. Shell thick walled, with irregular, roundish 

 pores, about as broad as the bars ; ten to twelve pores on the half equator. Surface spiny. Length 

 of the conical straight spines increasing towards the poles ; each polar spine surrounded by a 

 circumpolar group of larger, somewhat curved spines. The larger polar spine equals in length the 

 major axis ; the smaller is scarcely half as long. (The figure, given by Bury, is not quite exact ; 

 there the spines are situated in the pores, instead of between them. In my specimen the polar 

 spines were not branched.) 



