CAI/URRA. 21 



180ft long x 9/t to 13/i thick. Oral nngle 120. Apical ray curved 

 slightly orally, sharply pointed, 80 p. long x 8 p. tliirk. 



fipicidff. 



< Fringe oxea, slender, hastate, straight except for a slight bend at the 

 junction of the spear-head. IGO/i to '240 p. long x 7 p. to $ p. thick. The 

 maximum thickness is just lclow the spear-head. 

 ) Stumpy, stout, hastate oxea, from just lx?lo\v the edge, similar to () 140/i 



to 160 ft long x 14 ft to 16 p. thick. 



(//) Small quadriradiates from the oscular edge. Basal my 180/i or leas x 8 p. 

 to 10 fu Paired rays equal, sharply pointed, bending slightly downwards, 

 70 p. to 100 p. long x 8/1 to 10 p. thick. Ural angle 155 to 100. Apical 

 ray short, sharply pointed, bent slightly orally. 



DKRMATRETON. 



Grantiids 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 



cirt-\. 



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

 Tenthreiwdes in the family Sycettidaf. 



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

 in Kigs. 61 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 

 tv|x> of cortex. The cortical spicules have developed from the distal spicules of 

 tlu' tubar skeleton. In Grantia the inter-canals are small, and the skeleton bridges 

 i iv. r them. In Dermatreton the inter-canals are too large to be bridged over, and 

 a reticulated cortex results. 



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

 I M-nt, 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 <>r gastral layer is supported by a special skeleton of Urge quadriradiates 

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

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

 cliaml>ers, 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. hodgsoni). 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 triradiates lie in inclined positions, more or less 

 eml>raciiig the rounded tops of the flagellated chaml>ers. It thus happens not 



