REPORT ON THE RADIOLARIA. 1483 



5. Artostrobus articulatus, n. sp. (PL 79, fig. 16). 



Shell subcylindrical, with elegant longitudinal ribs and five sharp strictures. All six joints 

 nearly equal in length, each with three or four transverse rows of small circular pores. The 

 middle joints twice as broad as long. Cephalis hemispherical, with a conical, oblique horn. 



Dimensions. Length of the shell (with six joints) 0'16 ; length of a single joint 0'02 to O03, 

 breadth O04 to 0'05. 



Habitat. Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms. 



Genus 646. Lithomitra, 1 Butschli/1882, Zeitschr. f. wiss. Zool., p. 529. 



Definition. S tichocorida (vel Stichocyrtida eradiata aperta) with cylindrical 

 shell, the upper pole of which is rounded, the lower truncate. Cephalis without horn. 



The genus Lithomitra differs from the preceding genus Artostrobus in the absence 

 of a cephalic horn, and therefore bears to it the same relation as Dictyomitra does to 

 Lithostrobus. In many species the joints are very short, and bear only a single trans- 

 verse row of pores, and since the constrictions between the joints are often very slight, 

 Lithomitra becomes very similar to the Dicyrtide Dictyocephalus. 



Subgenus 1. Lithomitrella, Haeckel. 



Definition. A single transverse row of small circular pores on each joint. (Some- 

 times on the uppermost joints two or three rows.) 



1. Lithomitra pachyderma, Biitschli. 



Lithomitra pachyderma, Biitschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 529. 

 Eucyrtidium pachyderma, Ehrenberg, 1875, AbhandL d k. Akad. d. Wiss. Berlin, p. 72, Taf. 



xi. fig. 21. 

 Eucyrtidium imbricatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 72, Taf. xi. 



fig. 22. 



Shell thick-walled, subcylindrical, with longitudinal ribs, slightly dilated in the middle, with ten 

 to twelve subequal joints. On the lower edge of each joint a single row of small circular pores. 

 No external strictures. This and the following species (though separated by Ehrenberg as four 

 different species) may be united. 



Dimensions. Length of the shell (with ten joints) Oil ; length of each joint O'Ol to 0'012, 

 breadth 0'04. 



Habitat. Fossil in Barbados. 



1 Lithomitra= Stone-cap; 



