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



5. Stylatractus carduus, Haeckel. 



Stylosplicm-a carduus, Ehrenberg, 1875, AblianH. A. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. 

 fig. 7. 



Cortical shell thin walled, spiny, with regulai-, circular pores, five times as broad as the bars ; 

 ten to twelve on the half equator. Polar spines conical, half as long as the main axis, at the base 

 broader than the pores. (The cortical shell is ellipsoidal as well as both medullary shells ; the 

 figure of Ehrenberg, as is generally the case, is more correct than his description. This interesting 

 species occurs in the Barbados rocks, with double as well as with simple medullary shell, and may 

 in the latter case be distinguished as Lithatradus carduelis.) 



Dimensions. — Major axis of the cortical shell 0-12 to 016, minor Ol to 014 ; pores O'Ol to 0'02, 

 bars 0-002 to 0-005 ; main axes of the ellipsoidal medullary shells 0-05 and 0-03 ; length of the 

 polar spines 0-06, basal breadth 0-02. 



Habitat. — FossU in the Tertiary rocks of Barbados. 



Subgenus 3. Stylatractona, Haeckel. 



Definition. — Network of the outer shell irregular, with meshes of different size or 

 form ; surface smooth, without thorns or papilte. 



6. Stylatractus variabilis, n. sp. 



Cortical shell thin walled, smooth, with irregular, roundi.sh pores, twice to six times as broad as 

 the bars ; twelve to sixteen on the half equator. Polar spines conical, about half as long as the 

 main axis, and as broad at the base as the inner medullary shell. (The size and form of the pores 

 and of the polar spines in this species are very variable, so that the i^roportions given are to be 

 understood as averages. 



Dimeyisions. — Major axis 0-13, minor axis O'll ; pores 0-004 to 0-012, bars 0-002; main axes 

 of the ellipsoidal medullary shells 0-07 and 0-04 ; length of the polar spines 0-06, basal breadth 

 0-03. 



Habitat. — Pacific, central area, Stations 272 to 274, depth 2350 to 2750 fathoms. 



7. Stylatractus sethoporus, n. sp. (PI. 17, figs. 2, 3). 



Cortical shell thick walled, smooth, with large irregular, roundish pores, twice to four times as 

 broad as the bars; seven to eight on the half equator. At the bottom of each pore a thin lamella 

 of silex, perforated by four- to six hregular, roundish, double-contoured porules. Medullar}' shells 

 resemble those of Stylatractus giganteus. Polar spines three-sided pyramidal ; their length and basal 

 thickness scarcely equal the diameter of the inner medullary shell. 



Biinensions. — Major axis 0-15, minor axis 0-13 ; pores 0-02, bars 0-005, porules 0-01 ; length of 

 the polar spines 0-04. 



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



