1604 THE VOYAGE OF H.M.S. CHALLENGER. 



from 0'2 to 0*3 mm., whilst their thickness is only 0'002 to 0'004 mm., often it is less 

 than O'OOl, rarely more than 0'005 mm. The nodal points of the network, in which six 

 threads are usually united, are more or less thickened, often stellate (PI. 108, figs. 9, 

 12, &c.). Sometimes they are pierced by a central pore. The thin threads are constantly 

 cylindrical, never edged or prismatic, very elastic and flexible ; usually they are 

 perfectly smooth, rarely spiny or thorny, sometimes provided with scattered cruciate 

 verticils of lateral branches, as in Sagena crucifera and in the first described form of 

 this family, Sagmarium trigonizon (compare my Monograph, 1862, Taf. xxvi. fig. 5). 



The surface of the spherical shell is smooth only in two genera of Sagosphaerida, in 

 Sagena and Sagmarium (PI. 108, figs. 2, 8). In the five other genera it is covered 

 either with radial spines, arising from the nodal points of the network, or with peculiar 

 cortical pyramids or tent-shaped elevations (PI. 108, figs. 1, 36, &c.). These 

 pyramids are of the same characteristic shape as in the similar Auloscena among the 

 Aulosphserida (PL 110, fig. 1); usually, however, they are less regular than in the 

 latter. The pyramids or tents are usually six-sided, often, however, they are also four- 

 sided or three-sided, more rarely five, seven or more sided. The edges of the pyramids 

 are formed by filiform bars similar to those which compose the original lattice-work of 

 the Sagosphserida. The cavity of the pyramids is quite simple in Sagoscena (figs. 1, 5, 6), 

 whilst in Sagenoscena and Sagoplegma a radial column arises in its axis, the thickened 

 axial rod (figs. 3, 4, 10). 



The radial spines, which arise either from the tops of the pyramids or from the 

 nodal points of the network, exhibit in the Sagosphserida a variety and elegance similar 

 to the closely allied Aulosphserida. Sometimes a single radial spine arises in each nodal 

 point or at the top of each pyramid (figs. 3, 4, 10) ; at other times two, three, or four 

 (rarely more) divergent spines (figs. 69, 12, 13). These are rarely quite simple, usually 

 provided with lateral and terminal branches. The lateral branches are either scattered 

 irregularly, or regularly disposed in elegant verticils, each of which is usually composed 

 of three or four short branches (PI. 108, figs. 9, 13). The terminal branches form 

 either a similar verticil, or a bunch or corona, composed of numerous radial secondary 

 spines. The distal ends of the terminal as well as of the lateral branches are rarely 

 simple, usually they are provided with a spinulate knob or with an elegant spathilla 

 (PI. 108, figs. 3, 9, 13). 



The central capsule of the Sagosphserida is comparatively small, as it also is in the 

 Aulosphaerida and Orosphserida. Its diameter is usually about one-third or one-fourth 

 that of the enveloping shell, between 0'2 and 0'3, often only 0'12 to 0'18, rarely more than 

 0'3 mm. It is surrounded on the oral half by a red or dark phseodium and separated from 

 the inner surface of the shell by the voluminous calymma. The subspherical nucleus 

 is usually about half as broad as the capsule. The three openings of the latter, the 

 large tubular astropyle and the two opposite lateral parapylse, exhibit the same shape 



