REPORT ON THE RADIOLAEIA. 1617 



fig. 5). Their length is usually between O'l and 0'2 mm., rarely less than 0'08, or more than 

 0'24 mm.; their diameter usually between 0'003 to 0'005, sometimes only 0'002 or less, 

 at other times O'OOG or more. In several species the tangential tubes are thinner in the 

 middle part, and thickened towards the two ends (PI. 109, figs. 3, 4). Each tube con- 

 sists of a thin cylindrical wall of silex, and of a jelly-mass filling up its cavity; in its 

 axis runs a very thin, straight or slightly curved thread of silica, the axial filament. 



The arrangement of the tangential tubes, which originally, in the simplest 

 Aulosphserida, lie tangentially in the spherical face of a simple lattice-sphere, exhibits 

 various secondary modifications, leading to various interesting generic forms. Two 

 genera only, Attlaria (with triangular meshes, PI. Ill, fig. 2) and Aulonia (with 

 polygonal meshes, PI. Ill, fig. 1) possess a smooth, perfectly simple lattice-sphere, and 

 may therefore be regarded as the ancestral genera of the two subfamilies. Two other 

 corresponding genera, the common Aulosphcera (PI. 109) and the rarer Aulastrum 

 (PL 111, fig. 3), differ from the former in the development of radial spines at the nodal 

 points of the simple lattice-sphere. Aulophacus may be developed from Aulosphcera 

 by shortening, Aulatractus, however, by prolongation of the vertical main axis (PI. Ill, 

 figs. G, 7). In two genera, Auloplegma and Aulodictyum, the latticed wall of the spherical 

 shell becomes thickened and spongy, an irregular framework being formed by tubes 

 connected in different directions (PI. Ill, fig. 8). The most remarkable and the most 

 elegant form, however, of the whole family is represented by Auloscena (PI. 110). 

 The entire surface of the spherical lattice-shell is here covered with numerous regular or 

 subregular pyramids, or tent-shaped elevations. Usually each pyramid is six-sided, and 

 surrounded by six other six-sided pyramids, their bases being separated by six triangular 

 meshes, which lie in the spherical face. A similar elegant form is developed among the 

 Sagosphserida in the genera Sagoscena, Sagenoscena and Sagoplegma (PI. 108, fig. 1). 

 The structure of Auloscena, however, is usually more regular, and in the top of each 

 pyramid a radial tube arises. 



The junction of the cylindrical tubes at the nodal points of the network is very 

 remarkable. Aularia, the simplest form of the family, exhibits at each nodal point the 

 union of six tangential tubes (PL 111, fig. 2) ; their ends are so pointed and truncated 

 that they are connected in the form of a regular six-radiate star ; the conical end of each 

 tube is separated from, and at the same time closely connected with, the adjacent conical 

 ends of the two neighbouring tubes by a thin septum, the astral or sutural septum. The 

 six astral septa compose together a six-radiate star, and in the centre of this star the six 

 axial filaments of the tubes are united. Their central union is surrounded by a small, 

 double-contoured circle, and this circle seems to be the perimeter of a small and flat 

 Cavity on the inside of the star, which we call shortly the " nodal cavity " (" die kleine 

 Vertiefung" according to Hertwig, loc. cit., p. 90). The nodal cavity of Aularia 

 probably possesses a central opening on its inside and six small surrounding pores, which 



(ZOOL. CHALL. EXP. PART XL. 1886.) R r 203 



