REPORT ON THE RADIOLARIA. 419 



7. Trochodiscus cingillum, n. sp. 



Disk with smooth surface, in the distal part radially sulcated. Pores regular, circular ; twelve 

 to thirteen on the radius. Marginal spines twenty to twenty-four, triangular, of equal size and 

 at regular distances, only one-fourth as long as the radius of the disk, connected at their broad base 

 by a solid equatorial girdle of the double breadth. (Similar to Hdiodiscus cingillum, PI. 33, fig. 7, 

 but without medullary shell.) 



Dimensions. Diameter of the disk 0'22, of the pores 0'004 ; length of the spines 0'02, basal 

 breadth 0'02. 



Habitat. South Pacific, Station 285, depth 2375 fathoms. 



Family XIX. PHACODISCIDA, Haeckel (Pis. 31-35). 



Phacodiscida, Haeckel, 1881, Prodromus, p. 456. 



Definition. Discoidea with simple extracapsular phacoid shell (or lenticular 

 latticed cortical shell), connected by radial beams with an intracapsular, simple or double, 

 concentric medullary shell, without chambered equatorial girdles. 



The family Phacodiscida comprises a large number of splendid forms (about a 

 hundred species), which agree with the preceding Cenodiscida in the possession of the 

 characteristic extracapsular "phacoid shell," but differ from them in having one or 

 two intracapsular " medullary shells " ; these concentric spherical medullary shells are 

 connected with the lenticular cortical shell or phacoid shell by means of radial beams 

 perforating the central capsule. The Phacodiscida bear therefore the same relation to 

 the Cenodiscida that the Disphserida and Trisphaerida do to the Monosphserida. 



Formerly several species belonging to this family were described by Ehrenberg and 

 Johannes Miiller, but not distinguished from the Sphseroidea, genus Haliomma (e.g., 

 Haliomma sol et Haliomma humboldtii of the former, Haliomma amphidiscus of the latter). 

 For these oldest known species I constituted in 1862 my genus Heliodiscus (Monogr. d. 

 Radio!., p. 436). Some other genera were afterwards (1875) figured by Ehrenberg as 

 Periphcena and Chilomma. The rich material of the Challenger revealed this family as 

 very polymorphic and widely distributed, so that in my Prodromus (1881, p. 457) 

 I could enumerate eighteen different genera of Phacodiscida. This number is here 

 reduced to fifteen, uniting several of them into one genus as " subgenera." 



The Medullary Shell of the Phacodiscida, or the intracapsular latticed shell, is either 

 simple and spherical, or double, composed of two concentric spheres, which are united by 

 a variable number of radial beams. We could distinguish therefore as two subfamilies the 

 Carpodiscida (with simple medullary shell) and the Thecodiscida (with double concentric 

 medullary shell) ; the former corresponding to the Carposphserida (or Dyosphceria], the 

 latter to the Thecosphaerida (or Triospheeria). But as this difference seems not to be so 

 important as the different shape of the disk margin, we prefer this latter as a character 



