REPORT ON THE RADIOLARIA. 793 



I 



more natural to unite these latter into another suborder as Cladophracta, and to 



separate them from the Sphserocapsida, which may be called Capsophractee. 



The Dorataspida (Pis. 134-138), the common ancestral stock of the Clad o- 

 p h r a c t a, in the definition here restricted embraces all those Acanthophracta 

 in which the spherical lattice-shell is simple and composed of the meeting branches of 

 twenty radial spines united in its centre. As already pointed out above, this family is 

 probably diphyletic, and embraces two subfamilies which have been derived originally 

 from two different forms of Acanthonid a the Diporaspida (with two opposite 

 apophyses on each spine) derived from the Phractacanthida, and the Tessaraspida (with 

 four crossed apophyses on each spine) derived from the Stauracanthida ; in the former 

 we find originally forty apophyses, in the latter eighty apophyses, by the meeting 

 branches of which the spherical lattice-shell originates. The four following families of 

 Acanthophracta have probably been derived from the Diporaspida. 



The Phractopeltida (PI. 133, figs. 1-6) differ from all other Acanthophracta 

 in the possession of a double lattice-shell, composed of two concentric spheres which are 

 united by the twenty radial spines meeting in the centre. As all Phractopeltida 

 possess originally only two apophyses on each radial spine, they must be derived from 

 the Diporaspida (OropJiaspis), and bear to them the same relation as the Dyosphaerida 

 do to the Monosphserida. As the spherical central capsule of the Phractopeltida is 

 enclosed between both shells, smaller than the outer, larger than the inner shell, the 

 latter may be called "medullary shell," the former "cortical shell." This family 

 represents among the Acanthophracta only the " Diplophracta," whilst all others 

 are " Haplophracta." 



The three families here characterised may be called together "Sphserophract a," 

 as their central capsule and the enveloping shell are constantly spherical (or the shell 

 sometimes an " endospherical polyhedron "). On the contrary the following three 

 families of Acanthophracta may be united as "Prunophract a," as their 

 central capsule and shell are never spherical, but either ellipsoidal or lenticular or of 

 another form. The common ancestral stock of this suborder are the Belouaspida, in 

 which the form of the central capsule and the enclosing lattice-shell is ellipsoidal ; they 

 are derived from the Dorataspida (and probably all from the subfamily Diporaspida) by 

 the prolongation of two opposite radial spines which are larger than the eighteen others ; 

 they are the two equatorial spines of the " hydrotomical axis" (compare above, p. 719, 

 and PI. 136, figs. 6-9). 



The Hexalaspida (PI. 139) represent a new and very remarkable family, distinguished 

 from all other Acanthophracta by the preponderating development of six stout 

 radial spines, which are much larger than the fourteen others. These six principal spines 

 lie in one meridian plane of the shell (in the " hydrotomical plane," p. 720), and are the 

 two opposite equatorial spines and the four appertaining polar spines of the same plane. 



(ZOOL. CHALL. EXP. PART XL. 1886.) Rl 100 



