CAT.('AT?EA. 21 



180/i long X 9/1 to ]:\IJL thick. < >ral angle l'JO. Apical ray curved 

 slightly orally, sharply pointed, 80 p. long X 8 p. thick. 



(r) Fringe oxca, slender, hastate, straight except for a slight bend at 



junction of the spear-head. IGO/i to 240 p long x 7 /u. to 9 ju. thick. The 



maximum thickness is just below the spear-head. 

 (/) Stumpy, stout, hastate oxea. from just below the edge, similar to (a) 140 ju, 



to 160 /A long X 1 4 p to lf> p thick. 

 (//) Small quadriradiates from the oscular edge. Basal ray 180ft or less x 8 p. 



to 10 p. Paired rays equal, sharply pointed, bending slightly down ward ;. 



70 /A to 100 p. long x 8/x to 10 p. thick. Ural angle 155 to 160. Apical 



ray short, sharply pointed, bent slightly orally. 



DERMATRETON. 



Gran tikis in which the radial chambers are "linked" so as to form a reticulated 

 pattern round the large inter-canals, and are covered with a continuous reticulated 

 cortex. 



The definition of this new genus in the family Grantiidae corresponds to that of 

 '1',-iitlii'i-innli-n in the family Sycettidae. 



The remarkable reticulated cortices of the two species in this genus are shown 

 in Figs. Gl and 71. The importance of the " linking " of the flagellated chambers 

 as a generic characteristic is emphasised by the fact that it produces a corresponding 

 type of cortex. The cortical spicules have developed from the distal spicules of 

 the tubar skeleton. In drantid the inter-canals are small, and the skeleton bridges 

 over them. In Dermatri'ton the inter-canals are too large to be bridged over, and 

 a reticulated cortex results. 



In both the species in this genus the sponge is in the form of a tube more or less 

 bent, of circular cross-section, the maximum diameter being near the middle. The 

 tube tapers gradually to the base, which is very small, and also to the upper end, 

 which terminates in the oscule. The interior of the tube forms the gastral cavity. 

 The inner or gastral layer is supported by a special skeleton of large quadriradiates 

 regularly arranged, with the basal ray pointing downwards and the apical ray 

 projecting into the gastral cavity. Outside the gastral layer stand the ilagdlated 

 chambers, pointing radially outwards and linked into a meshwork pattern. They 

 communicate with the gastral cavity either independently (D. chartaceum] or in 

 groups through excurrent chambers (D. /i</</x<>iti). The distal ends of the flagellated 

 chambers are covered by a reticulated cortex, which follows the " linked " pattern of 

 the chambers. Many of the dermal triradjates lie in inclined positions, more or less 

 embracing the rounded tops of the flagellated chambers. 1 1 thus happens not 



