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



are to be seen in some Phaeosphseria (Oroplegma, PL 107, fig. 1; Sagoplegma, 

 PI. 108, fig. 2; Auloplegma, PI. Ill, fig. 8). No Spongoid skeletons are known 

 among the ACANTHARIA. 



127. The Cannoid Skeleton. Cannoid or tubular skeletons are those which are com- 

 posed of hollow tubes; they occur exclusively in the PHLEODARIA or CANNOPYLEA. 

 Tubular processes, nevertheless, occur in some other Radiolaria, as, for example, among 

 the SPUMELLARIA in a portion of the Collosphserida (Siphonosphcera, Caminosphcera, 

 Pis. 6, 7), and of the Prunoidea (Pipetta, Cannartus, &c., PL 39, figs. 6-10, &c.), 

 also among the NASSELLAEIA in Theosyringium (PL 68, figs. 4-6), Cannobotrys (PL 96, 

 figs. 3, 4, 8-11, 20-22), &c. In all these cases, however, the tubes are direct processes 

 of the cavity of the shell, the trabeculae of the lattice-work being solid. Only in the 

 CANNOPYLEA are the lattice-bars themselves, the radial spines and appendicular organs, 

 generally tubular (hence the designation " Pansolenia "). The lumen of the thin-walled 

 siliceous tubes is filled with jelly, and hence the specific gravity of the relatively large 

 skeleton is considerably diminished. This peculiarity is not found in all CANNOPYLEA ; it 

 is wanting in all Sagosphserida and Concharida, as well as in a part of the Orosphserida 

 and Castanellida ; in the latter there are found intermediate stages between hollow and 

 solid skeletal rods. Very often a fine siliceous thread runs in the axis of the tubes, which 

 is connected with its wall by lateral branches (PL 110, figs. 4, 6 ; PL 115, figs. 6, 7). 

 More seldom the tubes are divided by horizontal septa into a series of chambers (Meduset- 

 tida, Pis. 118-120). The two families Aulosphserida (Pis. 109-111) and Canno- 

 sphserida (PL 112) are distinguished from all other PH^ODARIA by the fact that their 

 tubes are separated by astral septa in the nodal points of the lattice-shell ( 112, 134). 



128. The Conchoid Skeleton. By the name " Conchoid skeletons" are distinguished 

 the bivalved lattice-shells which occur exclusively in the legion PH^ODAEIA ; they are 

 quite characteristic of the Phseoconchia or Phceodaria bivalvia, which embrace 

 three families : Concharida (Pis. 123-125), Ccelodendrida (Pis. 121, 122), and 

 Ccelographida (Pis. 126-128). The two valves of the lattice-shell of the Concharida 

 are simple, hemispherical, or boat-shaped, whilst in the Ccelodendrida and Coelographida 

 tubes grow out from them, which branch and usually give rise by anastomosis to a second 

 external bivalved shell. In all Phaeo. conchia the two valves are so disposed about 

 the central capsule that an open slit remains between them, into which open the apertures 

 of the central capsule ; and since all these Phceodaria conchoidea are TRIPYLEA, with three 

 typical openings in the central capsule, and since the two lateral accessory openings lie 

 at either side of the aboral pole, and the unpaired main-opening at the oral pole of the 

 main axis, it follows that the two valves are to be regarded as dorsal and ventral as in 

 the Brachiopoda (not right and left as in the Lamellibranchiata). The dorsal and ventral 



